chemistry an illustrated guide to science

CHEMISTRYSCIENCE VISUAL RESOURCES

An Illustrated Guide to Science

The Diagram Group

Chemistry: An Illustrated Guide to Science

Copyright © 2006 The Diagram Group

Author: Derek McMonagle BSc PhD CSci CChem FRSC

Editors: Eleanora von Dehsen, Jamie Stokes, Judith Bazler

Design: Anthony Atherton, Richard Hummerstone, Lee Lawrence, Phil Richardson

Illustration: Peter Wilkinson

Picture research: Neil McKenna

Indexer: Martin Hargreaves

All rights reserved. No part of this book may be reproduced or utilized in any formor by any means, electronic or mechanical, including photocopying, recording, orby any information storage or retrieval systems, without permission in writing fromthe publisher. For information contact:

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ISBN 0-8160-6163-7

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This book is printed on acid-free paper.

IntroductionChemistry is one of eight volumes of the Science Visual Resourcesset. It contains eight sections, a comprehensive glossary, a Web siteguide, and an index.

Chemistry is a learning tool for students and teachers. Full-colordiagrams, graphs, charts, and maps on every page illustrate theessential elements of the subject, while parallel text provides keydefinitions and step-by-step explanations.

Atomic Structure provides an overview of the very basic structureof physical matter. It looks at the origins of the elements andexplains the nature of atoms and molecules.

Elements and Compounds examines the characteristics of theelements and their compounds in detail. Tables give the boilingpoints, ionization energies, melting points, atomic volumes, atomicnumbers, and atomic masses key elements. Plates also describecrystal structures and covalent bonding.

Changes in Matter is an overview of basic chemical processes andmethods. It looks at mixtures and solutions, solubility,chromatography, and the pH scale.

Patterns—Non-Metals and Patterns—Metals focus on theproperties of these two distinct groups of elements. These sectionsalso include descriptions of the industrial processes used whenisolating important elements of both types.

Chemical Reactions looks at the essential factors that influencereactions. It includes information on proton transfer, electrolysis,redox reactions, catalysts, and the effects of concentration andtemperature.

Chemistry of Carbon details the chemical reactions involvingcarbon that are vital to modern industry—from the distillation ofcrude oil to the synthesis of polymers and the manufacture ofsoaps and detergents. This section also includes an overview of thechemistry of life.

Radioactivity is concerned with ionizing radiation, nuclear fusion,nuclear fission, and radioactive decay, as well as the properties ofradiation. Tables describe all known isotopes, both radioactive andnon-radioactive.

Contents

8 Formation of stars9 Fate of stars

10 The solar system11 Planet composition12 Planetary density, size, and

atmosphere13 Atomic structure14 Geiger and Marsden’s

apparatus15 Investigating the electron 116 Investigating the electron 217 Cathode ray oscilloscope

18 Measuring the charge on theelectron

19 Size and motion ofmolecules

20 Determination of Avogadro’sconstant

21 The mole22 Atomic emission spectrum:

hydrogen23 Energy levels: hydrogen

atom24 Luminescence

1 ATOMIC STRUCTURE

25 Organizing the elements26 The periodic table27 First ionization energies of

the elements28 Variation of first ionization

energy29 Melting points of the

elements °C30 Variation of melting

points31 Boiling points of the

elements °C32 Variation of boiling points33 Atomic volumes of the

elements34 Variation of atomic

volumes 35 Atomic mass

36 Periodic table with massesand numbers

37 Calculating the molecularmass of compounds

38 Structure of some ioniccrystals

39 Crystal structure of metals:lattice structure

40 Crystal structure of metals:efficient packing

41 Chemical combination: ionicbonding

42 Chemical combination: ionicradicals

43 Chemical combination:covalent bonding

44 Chemical combination:coordinate bonding

2 ELEMENTS AND COMPOUNDS

45 Mixtures and solutions46 Colloids47 Simple and fractional

distillation48 Separating solutions49 Paper chromatography

50 Gas-liquid chromatographyand mass spectrometry

51 The pH scale52 Indicators53 Titration of strong acids54 Titration of weak acids

3 CHANGES IN MATTER

55 pH and soil56 The water cycle57 Treatment of water and

sewage58 The water molecule59 Water as a solvent of ionic

salts

60 Ionic solutions61 Solubility62 Solubility curves63 Solubility of copper(II)

sulfate

64 Hydrogen: preparation65 Hydrogen: comparative

density66 Hydrogen: reaction with

other gases67 Hydrogen: anomalies in

ammonia and water68 Basic reactions of hydrogen69 The gases in air70 Nitrogen71 Other methods of

preparing nitrogen72 The nitrogen cycle73 Preparation and properties

of ammonia74 Industrial preparation of

ammonia (the Haberprocess): theory

75 Industrial preparation ofammonia (the Haberprocess): schematic

76 Industrial preparation ofnitric acid

77 Nitrogen: reactions inammonia and nitric acid

78 Basic reactions of nitrogen79 Nitrate fertilizers80 Oxygen and sulfur81 Extraction of sulfur—the

Frasch process

82 Oxygen and sulfur:allotropes

83 Oxygen and sulfur:compound formation

84 The oxides of sulfur85 Industrial preparation of

sulfuric acid (the contactprocess): theory

86 Industrial preparation ofsulfuric acid (the contactprocess): schematic

87 Affinity of concentratedsulfuric acid for water

88 Oxygen and sulfur:oxidation and reduction

89 Basic reactions of oxygen90 Basic reactions of sulfur91 The halogens: group 792 Laboratory preparation of

the halogens93 Compounds of chlorine94 Hydrogen chloride in

solution95 Acid/base chemistry of the

halogens96 Redox reactions of the

halogens97 Reactivity of the halogens

4 PATTERNS—NON-METALS

98 World distribution of metals99 Main ores of metals

100 The group 1 metals

101 The group 1 metals: sodium

102 The group 2 metals

5 PATTERNS—METALS

119 Reactivity of metals 1120 Reactivity of metals 2121 Electrolysis122 Electrolysis: electrode

activity and concentration123 Acids: reactions124 Preparation of acids125 Bases: reactions126 Bases: forming pure salts127 Proton transfer:

neutralization of alkalis128 Proton transfer:

neutralization of bases129 Proton transfer: metallic

carbonates130 Proton transfer:

neutralization of acids131 Collision theory132 Rates of reaction: surface

area and mixing133 Rates of reaction:

temperature andconcentration

134 Rates of reaction:concentration over time

135 Rate of reaction vs.concentration

136 Variation of reaction rate137 Rates of reaction: effect of

temperature 1138 Rates of reaction: effect of

temperature 2139 Exothermic and

endothermic reactions140 Average bond dissociation

energies141 Catalysts: characteristics142 Catalysts: transition

metals143 Oxidation and reduction144 Redox reactions 1145 Redox reactions 2146 Demonstrating redox

reactions147 Assigning oxidation state

6 CHEMICAL REACTIONS

103 The group 2 metals: generalreactions

104 The transition metals:electron structure

105 The transition metals:ionization energies andphysical properties

106 Aluminum107 Iron: smelting108 The manufacture of steel109 Rusting110 Copper smelting and

converting

111 Reactions of copper112 Reaction summary:

aluminum, iron, and copper113 The extraction of metals

from their ores114 Reactivity summary:

metals115 Tests on metals: flame test116 Tests on metals: metal

hydroxides117 Tests on metals: metal ions118 Uses of metals

148 The allotropes of carbon:diamond and graphite

149 The allotropes of carbon:fullerenes

150 The carbon cycle

151 Laboratory preparation ofcarbon oxides

152 The fractional distillation ofcrude oil

153 Other refining processes

7 CHEMISTRY OF CARBON

175 Ionizing radiation176 Radiation detectors177 Properties of radiations:

penetration and range178 Properties of radiations: in

fields179 Stable and unstable

isotopes180 Half-life181 Measuring half-life182 Radioactive isotopes183 Nuclear fusion184 Nuclear fission185 Nuclear reactor186 The uranium series187 The actinium series188 The thorium series

189 The neptunium series190 Radioactivity of decay

sequences191 Table of naturally occurring

isotopes 1 192 Table of naturally occurring

isotopes 2 193 Table of naturally occurring

isotopes 3194 Table of naturally occurring




isotopes 7

8 RADIOACTIVITY

198 Key words205 Internet resources207 Index

APPENDIXES

154 Carbon chains155 Naming hydrocarbons156 Table of the first six alkanes157 Table of the first five

alkenes158 Ethene159 Polymers160 Polymers: formation161 Polymers: table of

properties and structure162 Functional groups and

homologous series163 Alcohols164 Carboxylic acids

165 Esters166 Soaps and detergents167 Organic compounds: states168 Functional groups and

properties 169 Reaction summary: alkanes

and alkenes170 Reaction summary: alcohols

and acids171 Optical isomerism172 Amino acids and proteins173 Monosaccharides174 Disaccharides and

polysaccharides

Formation of starsATOMIC STRUCTURE

Big Bangblack holebrown dwarfneutron starprotostar

supernovawhite dwarf

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Hydrogen and helium

Collected mass of liquidhydrogen and helium

Nuclear reaction(hydrogen → helium)

Nuclear reaction(helium → carbon → iron)

Nuclear reaction(hydrogen → carbon)

Many heavy elements+ neutron star

Big Bang

Supernovaexplosion

Gravity

1 × Sun 10 × Sun 10(+)× SunToo little

(Brown dwarf)

White dwarf(carbon)

Blackhole

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Beginnings According to the Big Bang theory, the

universe resulted from a massiveexplosion that created matter, space,and time.

During the first thee minutes followingthe Big Bang, hydrogen and heliumwere formed as the universe began tocool.

Initial formation Stars were formed when gravity caused

clouds of interstellar gas and dust tocontract. These clouds became denserand hotter, with their centers boilingat about a million kelvins.

These heaps became round, glowingblobs called protostars.

Under the pressure of gravity,contraction continued, and a protostargradually became a genuine star.

A star exists when all solid particleshave evaporated and when light atomssuch as hydrogen have begun buildingheavier atoms through nuclearreactions.

Some cloud fragments do not have themass to ignite nuclear reactions. Thesebecome brown dwarfs.

The further evolution of stars dependson their size (See page 9).

Stars the size of our Sun will eventuallyshed large amounts of matter andcontract into a very dense remnant—awhite dwarf, composed of carbon andoxygen atoms.

More massive stars collapse quicklyshedding much of their mass indramatic explosions calledsupernovae. After the explosion, theremaining material contracts into anextremely dense neutron star.

The most massive stars eventuallycollapse from their own gravity toblack holes, whose density is infinite.

ATOMIC STRUCTUREFate of starsblack holefusionneutron starred giant

supernovawhite dwarf

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Fate of stars During most of a star’s life, the

outward pressure from nuclear fusionbalances the pull of gravity, but asnuclear fuel is exhausted, gravitycompresses the star inward and thecore collapses. How and how far itcollapses depends on the size of thestar.

1 The fate of a star thesize of our sun A star the size of our Sun burns

hydrogen into helium until thehydrogen is exhausted and the corebegins to collapse. This results innuclear fusion reactions in a shellaround the core. The outer shell heatsup and expands to produce a redgiant.

Ultimately, as its nuclear reactionssubside, a red giant cools andcontracts. Its core becomes a verysmall, dense hot remnant, a whitedwarf.

2 Fate of a larger star Stars with an initial mass 10 times that

of our Sun go further in the nuclearfusion process until the core is mostlycarbon. The fusion of carbon intolarger nuclei releases a massiveamount of energy. The result is a hugeexplosion in which the outer layers ofthe star are blasted out into space.This is called a supernova.

After the explosion, the remainingmaterial contracts, and the corecollapses into an extraordinary denseobject composed only of neutrons—a neutron star.

3 Fate of a massive star Stars with an initial mass of 30 times

our Sun undergo a different fatealtogether. The gravitational field ofsuch stars is so powerful that materialcannot escape from them. As nuclearreactions subside, all matter is pulledinto the core, forming a black hole.

Time

Time

Time

1 The fate of a star the size of our suna b c d

g

j k

l m n

e f

i

h

2 Fate of a larger star

3 Fate of a massive star

a hydrogen is converted to heliumb planetary system evolvesc hydrogen runs out and helium is converted

to carbond star cools to form a red giante carbonf star evolves to form a white dwarfg hydrogen is converted to helium and carbon,

and eventually ironh hydrogen runs out, and star undergoes

gravitational collapse

i The collapsed star suddenly expands rapidly,creating a supernova explosion

j creates many different elementsk the core of the dead star becomes a neutron

starl hydrogen converted to many different

elementsm hydrogen runs out, and the star collapses to

form a black holen black hole

m liquid hydrogen and heliumn small rocky centero radii:

Jupiter = 11 × radius of EarthSaturn = 9 × radius of Earth

f light shellg dense coreh light shelli dense core

1 Birth of the solar system

a

b

c

d

h

k

l

e

i

3 Inner planetsMercury

Uranus andNeptune

j

j diameter = 2 or 3 that of the Earthk solid water, methane, and ammonial liquid water, methane, and ammonia

a hydrogen and heliumb heavier elementsc lighter elements

d denser inner planetse less dense outer planets

Jupiter andSaturn

m

n

o

Mars

4 Outer planets

gf

2 Formation of the innerand outer planets

The solar systemATOMIC STRUCTURE

1 Birth of the solar system The solar system is thought to have

formed about 4.6 billion years ago as aresult of nuclear fission in the Sun.

A nebula (cloud) of gases and dustthat resulted from the explosion.flattened into a disk with a highconcentration of matter at the center.

2 Formation of the innerand outer planets Near the Sun, where the temperature

was high, volatile substances could notcondense, so the inner planets(Mercury, Venus, Earth, and Mars) aredominated by rock and metal. Theyare smaller and more dense than thosefarther from the Sun.

In the colder, outer areas of the disk,substances like ammonia andmethane condensed, while hydrogenand helium remained gaseous. In thisregion, the planets formed (Jupiter,Saturn, Uranus, and Neptune) weregas giants.

3 Inner planets Inner planets consist of a light shell

surrounding a dense core of metallicelements.

Mercury, the planet closest to the Sun,has a proportionately larger core thanMars, the inner planet farthest fromthe Sun.

4 Outer planets The outer planets have low densities

and are composed primarily ofhydrogen and helium.

The outer planets are huge incomparison to the inner planets.

Jupiter and Saturn, the largest of thegas giants, contain the greatestpercentages of hydrogen and helium;the smaller Uranus and Neptunecontain larger fractions of water,ammonia, and methane.

ammoniafissionheliumhydrogenmethane

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ATOMIC STRUCTURE

1 Basic composition of theplanets The inner planets—Mercury, Venus,

Earth, and Mars—consist of aniron–nickel core surrounded by a shellof silicon and other elements.

The outer planets—Jupiter, Saturn,Uranus, and Neptune—consist largelyof solid or liquid methane, ammonia,liquid hydrogen, and helium.

Pluto is not included in thiscomparison because it is atypical ofthe other outer planets, and its originsare uncertain.

2 Composition of Earth Earth consists of a dense, solid inner

core and a liquid outer core of nickeland iron. The core is surrounded bythe mantle (a zone of dense, hotrock), and finally by the crust, which isthe surface of Earth.

Since most of the materials of Earthare inaccessible (the deepest drilledholes only penetrate a small distanceinto the crust), we can only estimatethe composition of Earth by looking atthe composition of the materials fromwhich Earth formed. Meteoritesprovide this information.

Oxygen is the most common elementon Earth, and about one fifth ofEarth’s atmosphere is gaseous oxygen.

Oxygen is also present in manycompounds, including water (H2O),carbon dioxide (CO2), and silica(SiO2), and metal salts such as oxides,carbonates, nitrates, and sulfates.

Planet compositionatmospherecarbonatecrustmantlenitrate

oxidesulfate

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a Mercuryb Venus

c Earthd Mars

e Jupiterf Saturn

g Uranush Neptune

1 Basic composition of the planets

a d

e

g h

i

j

k

l

m

n

b c

f

Composition %of Earth

oxygen 46silicon 28aluminum 8iron 5calcium 4sodium 3potassium 3magnesium 2

Solid/liquid water, methane, and ammonia

2 Composition of Earth

Liquid hydrogen and helium

Iron/nickel core shell of silicon and other elements

i crustj mantle (oxygen, silicon, aluminum, iron)k outer core (liquid – nickel and iron)

l inner core (solid – nickel and iron)m crust, mantle, and oceans = 2/3 of mass)n core = 1/3 of mass

Den

sity

(rel

ativ

eto

wat

er)

4

3

2

5

1

7

6

Rad

ius

(in

km)

1 Densities and radii of the planets

40,000

30,000

20,000

50,000

10,000

70,000

60,000

02,000

Distance from Sun (in millions of miles)1,000 3,000

2 Atmospheric composition of the inner planets

Carbon dioxide

Nitrogen

Oxygen

Others

Venus Mars

Earth

a Mercuryb Venusc Earth

d Marse Jupiterf Saturn

g Uranush Neptune

a

b

c

d

h

f

a

b

c

d

e

e

f

g

g

h

Radius

Density

Planetary density, size,and atmosphere

ATOMIC STRUCTURE

1 Densities and radii of theplanets The inner planets—Mercury, Venus,

Earth, and Mars—are relatively smallbut have a higher density than theouter planets.

The outer planets—Jupiter, Saturn,Uranus, and Neptune—are relativelylarge but have a lower density than theinner planets.

2 Atmospheric compositionof the inner planets Earth’s atmosphere was probably

similar to that of Venus and Mars whenthe planets formed. However, theparticular conditions on Earth allowedlife to start and flourish. With thiscame drastic changes to thecomposition of the atmosphere. Ofparticular importance is the evolutionof green plants.

Green plants contain a pigment calledchlorophyll. Plants use this pigment totrap energy from sunlight and makecarbohydrates. The process is calledphotosynthesis.

As Earth became greener, theproportion of carbon dioxide in theatmosphere fell until it reached thepresent level of about 0.04 percent.

The green plants provided a means ofturning the Sun’s energy into food,which in turn, provided animals withthe energy they needed to survive.Thus, animals could evolve alongsideplants.

Conditions on the two planetsadjacent to Earth—Venus and Mars—were not suitable for life as we knowit, and the atmospheres on theseplanets have remained unchanged.

atmospherecarbon dioxidechlorophyllphotosynthesis

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ATOMIC STRUCTURE

1 Principle subatomicparticles An atom is the smallest particle of an

element. It is made up of even smallersubatomic particles: negativelycharged electrons, positively chargedprotons, and neutrons, which have nocharge.

2 The atom An atom consists of a nucleus of

protons and neutrons surrounded by a number of electrons.

Most of the mass of an atom iscontained in its nucleus.

The number of protons in the nucleusis always equal to the number ofelectrons around the nucleus. Atomshave no overall charge.

3 Representing an element Elements can be represented using

their mass number, atomic number,and atomic symbol:mass numberatomic number Symbol

The atomic number of an atom is thenumber of protons in its nucleus.

The mass number is the total numberof protons and neutrons in its nucleus.Thus, an atom of one form of lithium(Li), which contains three protons andfour neutrons, can be represented as: 73Li

4 Isotopes All atoms of the same element have

the same atomic number; however,they may not have the same massnumber because the number ofneutrons may not always be the same.Atoms of an element that havedifferent mass numbers are calledisotopes. The diagram at left illustratesisotopes of hydrogen.

Atomic structureatomatomic numberelectronisotopemass number

neutronnucleusprotonsubatomic

particle

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+

++

73Li

+

++

+

+++

+

+

+

++

1 Principle subatomic particles

11836

Particle Relative atomic mass Relative charge

Electron

Neutron

Proton

1

1

0

1

–1

2 The atom

3 Representingan element

4 Isotopes

+

Hydrogen 1

+

Hydrogen 2

+

Hydrogen 3

proton

neutronnucleus

electron

Geiger and Marsden’sapparatus

ATOMIC STRUCTURE

Developing the atomicmodel At end of the 19th century, scientists

thought that the atom was a positivelycharged blob with negatively chargedelectrons scattered throughout it. Atthe suggestion of British physicistErnest Rutherford, Johannes Geigerand Earnest Marsden conducted anexperiment that changed this view ofthe atomic model.

Scientists had recently discovered thatsome elements were radioactive—theyemitted particles from their nuclei as aresult of nuclear instability. One typeof particle, alpha radiation, is positivelycharged. Geiger and Marsdeninvestigated how alpha particlesscattered by bombarding them againstthin sheets of gold, a metal with a highatomic mass.

They used a tube of radon, aradioactive element, in a metal block(a) as the source of a narrow beam ofalpha particles and placed a sheet ofgold foil in the center of theirapparatus (b). After they bombardedthe sheet, they detected the pattern ofalpha particle scattering by using afluorescent screen (c) placed at thefocal length of a microscope (d).

If the existing model had been correct,all of the particles would have beenfound within a fraction of a degree ofthe beam. But Geiger and Marsdenfound that alpha particles werescattered at angles as large as 140°.

From this experiment, Rutherforddeduced that the positively chargedalpha particles had come into therepulsive field of a highly concentratedpositive charge at the center of theatom. He, therefore, concluded that anatom has a small dense nucleus inwhich all of the positive charge andmost of the mass is concentrated.Negatively charged electrons surroundthe nucleus—similar to the way theplanets orbit the Sun.

alpha particleatomatomic mass

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db

a

c

a source of alpha particles (radon tube)b gold foilc screend microscope

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ATOMIC STRUCTURE

Investigating the electron During the last half of the nineteenth

century, scientists observed that whenan electric current passes through aglass tube containing a small amountof air, the air glowed. As air wasremoved, a patch of fluorescenceappeared on the tube, which theycalled cathode rays. Scientists thenbegan investigated these streams ofelectrons traveling at high speed.

1 Maltese cross tube In the 1880s, William Crookes

experimented on cathode rays using aMaltese cross tube.

The stream of electrons emitted by thehot cathode is accelerated toward theanode. Some are absorbed, but themajority passes through and travelsalong the tube. Those electrons thathit the Maltese cross are absorbed.Those electrons that miss the crossstrike the screen, causing it tofluoresce with a green light.

The result of this experiment is that ashadow of the cross is cast on thescreen. This provides evidence thatcathode rays travel in straight lines.

2 The Perrin tube In 1895 Jean Perrin devised an

experiment to demonstrate thatcathode rays convey negative charge.

He constructed a cathode ray tube inwhich the cathode rays wereaccelerated through the anode, in theform of a cylinder open at both ends,into an insulated metal cylinder calleda Faraday cylinder.

This cylinder has a small opening atone end. Cathode rays enter thecylinder and build up charge, which isindicated by the electroscope. Perrinfound that the electroscope hadbecome negatively charged.

Perrin’s experiments helped toprepare the way for English physicistJ. J. Thompson’s work on electrons afew years later.

anodecathodecathode rays

electronfluorescence

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Investigating the electron 1

a E.h.t. supplyb low voltagec heated filament and cathoded anode

e Maltese-Cross (connected to anode)g shadowh invisible cathode raysf fluorescent screen

––

––

+

–

– – –

+

–

– +

+

i

j l n

p

m

q

o

+

–

–+

2 The Perrin tube

1 Maltese-Cross tubea

b c d gh e

f

k

i E.h.t. supplyj 6 V supplyk cathodel anodem track of electron beam in magnetic field

n vacuumo gold-leaf electroscopep electrons are collectedq insulated metal cylinder

Investigating the electron 2

ATOMIC STRUCTURE

1 J.J. Thomson’s cathoderay tube In 1897 J.J. Thomson devised an

experiment with cathode rays thatresulted in the discovery of theelectron.

Up to this time, it was thought that thehydrogen atom was the smallestparticle in existence. Thomsondemonstrated that electrons (which hecalled corpuscles) comprising cathoderays were nearly 2,000 times smaller inmass than the then lightest-knownparticle, the hydrogen ion.

When a high voltage is placed across apair of plates, they become chargedrelative to each other. The positivelycharged plate is the anode, and thenegatively charged plate the cathode.

Electrons pass from the surface of thecathode and accelerate toward theoppositely charged anode. The anodeabsorbs many electrons, but if theanode has slits, some electrons willpass through.

The electrons travel into an evacuatedtube, where they move in a straightline until striking a fluorescent screen.This screen is coated with a chemicalthat glows when electrons strike it.

2 Evidence of thephotoelectric effect The photoelectric effect is the

emission of electrons from metalsupon the absorption ofelectromagnetic radiation.

Scientists observed the effect in thenineteenth century, but they could notexplain it until the development ofquantum physics.

To observe the effect, a clean zincplate is placed in a negatively chargedelectroscope. The gold leaf and brassplate carry the same negative chargeand repel each other.

When ultraviolet radiation strikes thezinc plate, electrons are emitted. Thenegative charge on the electroscope isreduced, and the gold leaf falls.

anodecathodecathode rayselectron

photoelectriceffect

radiation

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+––– +

++

+––

–

––

–– ––

–

–

–

––––

2 Evidence of the photoelectric effect

++ +++

Negatively chargedelectroscope withzinc plate attached

The leaf falls aselectrons are ejectedfrom the zinc plate

If positively chargedthe electroscoperemains charged

1 J.J. Thomson’s cathode ray tube

a

b c d i

k l

o

n

f h

m

– +

k mercury vapor lampl ultraviolet lightm brass plate

n gold leafo zinc plate

e

j

g

a high voltageb cathodec gas discharge provides free electronsd anode with slite y-deflecting plate

f direction of travel of the cathode raysg flourescent screenh lighti evacuated tubej x-deflecting plate

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ATOMIC STRUCTURE

1 Cathode ray oscilloscope The cathode ray oscilloscope (CRO) is

one of the most important scientificinstruments ever to be developed. It isoften used as a graph plotter to displaya waveform showing how potentialdifference changes with time. TheCRO has three essential parts: theelectron gun, the deflecting system,and the fluorescent gun.

The electron gun consists of a heaterand cathode, a grid, and severalanodes. Together these provide astream of cathode rays. The grid is atnegative potential with respect to thecathode and controls the number ofelectrons passing through its centralhole. It is the brightness control.

The deflecting system consists of a pairof deflecting plates across whichpotential differences can be applied.The Y-plates are horizontal but deflectthe beam vertically. The X-plates arevertical and deflect the beanhorizontally.

A bright spot appears on thefluorescent screen where the beamhits it.

2 Electron gun When a current passes through the

heater, electrons are emitted from thesurface of the cathode and attractedtowards an oppositely charged anode.Some will be absorbed by the anode,while others pass through and areaccelerated, forming a stream of high-speed electrons.

Cathode ray oscilloscopeanodecathodecathode rays

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– – –

+

+

1 The cathode ray oscilloscope

c d

i

a

l k j

e

h

f

g

b

a heaterb y-deflection platesc y-input terminald x-input terminale x-deflection platesf light

g phosphor coatingh electron beami common-input terminalj accelerating and focusing anodesk gridl cathode

2 Electron gun

w

m n o p

v t s qru

– +

m low voltagen heatero cathodep cyclindrical anodeq high speed electronsr accelerated electronss anode

t cathodeu evacuated tubev electron beamw high voltage

Measuring the charge onthe electron

ATOMIC STRUCTURE

Measuring the charge onthe electron In the early part of the 20th century,

American physicist Robert Millikanconstructed an experiment toaccurately determine the electriccharge carried by a single electron.

Millikan’s apparatus consisted of twohorizontal plates about 20 cm indiameter and 1.5 cm apart, with asmall hole in the center of the upperplate.

At the beginning of the experiment, anatomizer sprayed a fine mist of oil onto the upper plate.

As a result of gravity, a droplet wouldpass through the hole in the plate intoa chamber that was ionized byradiation. Electrons from the airattached themselves to the droplet,causing it to acquire a negative charge.A light source illuminated the droplet,making it appear as a pinpoint of light.Millikan then measured its downwardvelocity by timing its fall through aknown distance.

Millikan measured hundreds ofdroplets and found that the charge onthem was always a simple multiple of abasic unit, 1.6 x 10-19 coulomb. Fromthis he concluded that the charge onan electron was numerically 1.6 x 10-19

coulomb.

electronradiation

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Millikan’s apparatus

c

d

f

h

b

a

g

e

j i

a sealed containerb atomizerc oil dropletsd charged metal plate (+)e charged oil droplets

f light sourceg viewing microscopeh charged metal plate (–)i ionizing radiationj power source

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ATOMIC STRUCTURE

1 Estimating the size of a molecule Scientists can estimate the size of a

molecule by dividing the volume of asphere by the volume of a cylinder.

In the example in the diagram, thevolume of a spherical oil drop ofradius, rs, is given by:4 x p x rs

3

3

When the oil drop spreads across thesurface of water, it takes the shape of acylinder of radius, rc, and thickness, h.The volume of such a cylinder is:p x rc

2 x h

If we assume that the layer of oil isone molecule thick, then h gives thesize of an oil molecule.

When spread on water the drop of oilwill have the same volume therefore:h = 4 x p x rs

3 x 1

3 p x rc2

h = 4 rs3

3 rc2

2 Brownian motion in air Brownian motion is the random

motion of particles through a liquid orgas. Scientists can observe this byusing a glass smoke chamber.

Smoke consists of large particles thatcan be seen using a microscope.

In the smoke chamber, the smokeparticles move around randomly dueto collisions with air particles.

3 Diffusion Diffusion is the spreading out of one

substance through another due to therandom motion of particles.

The diagram illustrates how scientistsuse a diffusion tube to observe this.Initially the color of the substance isstrongest at the bottom of the tube.

After a period of time, as a result ofdiffusion, the particles of thesubstance mix with air particles, andthe color becomes uniform down thelength of the tube.

Brownian motiondiffusionmolecule

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1 Estimating the size of a molecule

a

b

c

d

g

h

j

k

l

m

n

o p

r

s

u

tq

e

f

ih

2 Brownian motion in air 3 Diffusion

a tapeb cardboardc fine stainless steel wired magnifying glasse 1/2 mm scalef view through magnifying

glassg oil droph waxed sticks

i wax-coated trayj lycopodium powderk oil patchl microscopem removable lidn windowo lampp glass rod for converging

light

q glass smoke chamberr glass diffusion tubes liquid bromine capsulet rubber stopperu tapv bromine capsulew rubber tubex point at which pressure is

applied to break capsule

Determining the radius ofan oil drop

Determining the radius of anoil drop spread

x v

w

Size and motion ofmolecules

Determination ofAvogadro’s constant

ATOMIC STRUCTURE

Defining Avogadro’sconstant Avogadro’s constant is the number of

particles in a mole of a substance. Itequals 6.023 x 1023 mol-1.

It is F, the Faraday constant—96,500coulombs per mole, the amount ofelectric charge of one mole ofelectrons—divided by 1.60 x 10-19

coulomb—the charge on one electron(expressed as e).

Thus, the Avogadro constant, N, isgiven by: N = F

e

or:96,500 = 6.023 x 1023 mol-1

1.60 x 10-19

Determining the Constant The number of molecules in one mole

of substance can be determined byusing electrochemistry.

During electrolysis, current (electronflow) over time is measured in anelectrolytic cell (see diagram). Thenumber of atoms in a weighed sampleis then related to the current tocalculate Avogadro’s constant.

Illustrating the Procedure The diagram illustrates the electrolysis

of copper sulfate. To calculateAvogadro’s constant, the researcherweighs the rod to be used as theanode before submerging the twocopper rods in copper sulfate. Shethen connects the rods to a powersupply and an ammeter (aninstrument used to measure electriccurrent). She measures and recordsthe current at regular intervals andcalculates the average amperage (theunit of electric current). Once sheturns off the current, she weighs theanode to see how much mass was lost.Using the figures for anode mass lost,average current, and duration of theelectrolysis, she calculates Avogadro’sconstant.

anodeAvogadro’s

constantelectrolysisFaraday constant

mole

Key words

20

A

– +

Determination of Avogadro’s constant

a b

c

d

e

f

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ATOMIC STRUCTURE

1 Defining a mole Because atoms, ions, and molecules

have very small masses, it is impossibleto count or weigh them individually. Asa result, scientists use moles in achemical reaction.

A mole is the amount of substancethat contains as many elementaryentities (atoms, molecules, ions, anygroup of particles) as there are atomsin exactly 0.012 kilogram of carbon-12.This quantity is Avogadro’s constant(6.023 x 1023 mol-1).

The significance of this number is thatit scales the mass of a particle inatomic mass units (amu) exactly intograms (g).

Chemical equations usually imply thatthe quantities are in moles.

2 Moles of gas One mole of any gas occupies

22.4 liters at standard temperature andpressure, (which is 0 ºC andatmospheric pressure).

The diagram shows the mass in gramsof one mole of the following gases:chlorine (Cl2), carbon dioxide (CO2),methane (CH4), hydrogen (H2),nitrogen (N2), and oxygen (O2).

3 Molarity Molarity is concerned with the

concentration of a solution. Itindicates the number of particles in1 liter of solution.

A 1 molar solution contains 1 mole ofa substance dissolved in water or someother solvent to make 1 liter ofsolution.

The diagram shows the mass in gramsof one mole of the followingsubstances: iron(II) chloride (FeCl2),magnesium chloride (MgCl2), bariumsulfate (BaSO4), sodium hydroxide(NaOH), calcium nitrate (Ca(NO3)2),and potassium bromide (KBr).

The moleatomionmolaritymolemolecule

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1 liter

6.023 × 1023 particles

1 Defining a mole

1 particle –

x amu x grams

(71 g) Cl2

(44 g) CO2

(16 g) CH4

H2 (2 g)

N2 (28 g)

O2 (32 g)

22.4 liters

(127 g) FeCl2

(95 g) MgCl2

(233 g) BaSO4

NaOH (40 g)

Ca(NO3)2 (164 g)

KBr (119 g)

2 Moles of gas

3 Molarity

Atomic emissionspectrum: hydrogen

ATOMIC STRUCTURE

Atomic spectrum The atomic emission spectrum of an

element is the amount ofelectromagnetic radiation it emitswhen excited. This pattern ofwavelengths is a discrete linespectrum, not a continuous spectrum.It is unique to each element.

Investigating hydrogen Toward the end of the nineteenth

century, scientists discovered thatwhen excited in its gaseous state, anelement produces a unique spectralpattern of brightly colored lines.Hydrogen is the simplest element and,therefore, was the most studied.Hydrogen has three distinctivelyobservable lines in the visiblespectrum—red, blue/cyan, and violet.

Series In 1885 Swiss mathematician and

physicist Johannes Jakob Balmerproposed a mathematical relationshipfor lines in the visible part of thehydrogen emission spectrum that isnow known as the Balmer series.

The series in the ultraviolet region ata shorter wavelength than the Balmerseries is known as the Lyman series.

The series in the infrared region atthe longer wavelength than the Balmerseries is known as the Paschen series.

The Brackett series and the Pfundseries are at the far infrared end of thehydrogen emission series.

atomic emissionspectrum

infraredspectrumultraviolet

wavelength

Key words

22

Emission spectrum in the near ultra-violet and visible

Schematic series

4.5686.1676.9077.309

ab c d e f

a

30 6 0.6

H° Hd Hg Hb H

Violet Red

a frequency (×1014Hz)b Lyman seriesc Balmer series

d Paschen seriese Bracket seriesf Pfund series

Balmer series

f

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ATOMIC STRUCTURE

Energy levels Electrons are arranged in definite

energy levels (also called shells ororbitals), at a considerable distancefrom the nucleus.

Electrons jump between the orbits byemitting or absorbing energy.

The energy emitted or absorbed isequal to the difference in energybetween the orbits.

Energy levels of hydrogen The graph shows the energy levels for

the hydrogen atom. Each level isdescribed by a quantum number(labeled by the integer n).

The shell closest to the nucleus hasthe lowest energy level. It is generallytermed the ground state. The statesfarther from the nucleus havesuccessively more energy.

Transition from n level toground state Transition from n=2 to the ground

state, n=1:Frequency =24.66 x 1014 Hz

Transition from n=3 to the groundstate, n=1:Frequency =29.23 x 1014 Hz

Transition from n=4 to the groundstate, n=1:Frequency =30.83 x 1014 Hz

Line spectrum This radiation is in the ultraviolet

region of the electromagneticspectrum and cannot be seen by thehuman eye.

Energy levels: hydrogenatom

ground stateorbitalquantum numbershellultraviolet

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Frequency / 1014 Hz

Ground state

Ene

rgy

Energy-level schematic

Line spectrum

n = ?

n = 5

n = 4

n = 3

n = 2

n = 1

30.83 29.23 24.66b ag

g b a

LuminescenceATOMIC STRUCTURE

1 Luminescence Luminescence is the emission of light

caused by an effect other than heat. Luminescence occurs when a

substance is stimulated by radiationand subsequently emits visible light.

The incident radiation exciteselectrons, and as the electrons returnto their ground state, they emit visiblelight.

If the electrons remain in their excitedstate and emit light over a period oftime, the phenomenon is calledphosphorescence.

If the electrons in a substance returnto the ground state immediately afterexcitation, the phenomenon is calledfluorescence.

2 Fluorescence In this diagram, a fluorescent light

tube contains mercury vapor at lowpressure. Electrons are released fromhot filaments at each end of the tubeand collide with the mercury atoms,exciting the electrons in the mercuryatoms to higher energy levels. As theelectrons fall back to lower energystates, photons of ultraviolet light areemitted.

The ultraviolet photons collide withatoms of a fluorescent coating on theinside of the tube. The electrons inthese atoms are excited and thenreturn to lower energy levels, emittingvisible light.

fluorescenceluminescencephosphorescence

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1 Luminescence

2 Fluorescence

E3

E2

E1

Ene

rgy

(E)

Photon

Photon

Secondexcitedstate

Firstexcitedstate

Groundstate

Electronabsorbsphoton

Electronemits

photon

n = 3

n = 2

n = 1

e–

e–

ultravioletphotonsare emitted

visible light filamentfilament

mercuryatoms

fluorescentcoating

Energylevels

ELEMENTS AND COMPOUNDS

1 Antoine Lavoisier In 1789, French chemist Antoine

Lavoisier organized what he believedwere the elements into four groups:Group 1 gases, Group 2 non-metals,Group 3 metals, and Group 4 earths.

2 Johann Dobereiner In 1817, German chemist Johann

Dobereiner noticed that the atomicmass of strontium was about half waybetween that of calcium and barium.After further study, he found that hecould organize other elements intosimilar groups based on the samerelationship to each other. He calledthese groups triads. Subsequently,scientists attempted to arrange all ofthe known elements into triads.

3 John Newlands In 1864, English chemist John

Newlands noticed that if the elementswere arranged in increasing order ofatomic mass, the eighth element afterany given one had similar properties.He likened this to an octave of musicand called the regularity the “law ofoctaves.”

Newlands’s arrangement worked wellfor the first 17 elements but brokedown thereafter. Consequently, it wasnot well received by other scientists.

4 Lothar Meyer In 1870, German chemist Lothar Meyer

plotted a graph of atomic volumeagainst atomic mass.

He found a pattern in which elementsof similar properties appeared insimilar positions on the graph.

Organizing the elementsatomic massatomic volumeelement

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4 Lothar Meyer

Ato

mic

volu

me/

cm3

mol

–1

80

60

Atomic number

35

60

40

20

00 5 10 15 20 25 30 40 45 50 55

Group 1 Group 2 Group 3 Group 4

heat

light

oxygen

nitrogen

sulfur

phosphorus

copper

tin

lead

zinc

lime

baryta

magnesia

alumina

silica

1 Antoine Lavoisier

Triad Relative atomic mass

Li

S

Cl

Ca

2 Johann Dobereiner

Na

Se

Br

Sr

K

Te

I

Ba

7

32

35.5

40

23

79

80

88

39

128

127

137

H

1

F

8

Cl

15

Li

2

Na

9

K

16

Be

3

Mg

10

Ca

17

B

4

Al

11

Cr

18

C

5

Si

12

Ti

19

N

6

P

13

Mn

20

O

7

S

14

Fe

21

3 John Newlands

The periodic tableELEMENTS AND COMPOUNDS

1 Mendeleyev’s periodictable The modern periodic table is based

on that developed by Russian chemistDmitry Mendeleyev in the 1860s.

He arranged the elements in order ofincreasing atomic mass. He called thehorizontal rows periods and thevertical columns groups. He groupedthe elements on the basis of theirproperties.

Mendeleyev made a separate group forthose elements that did not appear tofit the pattern. He also left spaceswhere there was no known elementthat fit the pattern and madepredictions about themissing elements.

There were some problemswith Mendeleyev’s table. Forexample, iodine was placedafter tellurium on the basisof its chemistry, eventhough its atomic mass waslower than tellurium. Also,there was no obvious placefor the noble gases. Theseproblems were subsequentlyresolved when, in 1914,English physicist HenryMoseley showed that theelements could be arrangedin a pattern on the basis oftheir atomic number.

2 The modernperiodic table Metals occupy positions to

the left and center, whilenon-metals are found to theright. Hydrogen is theexception to this pattern.The atomic structure ofhydrogen would indicatethat it belongs at the top leftof the table; however, it is anon-metal and has verydifferent properties fromthe group 1 elements.

atomic massatomic numberelementgroupgroup 1

noble gasesperiodperiodic table

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Metals

Semi-metals

Non-metals

Spaces were left for elements that had not been discovered. They were candium, gallium,germanium, and technetium.

1 Part of Mendeleyev’s periodic table

2 Modern Periodic Table

H

Li

Na

K

Cu

Rb

Ag

Be

Mg

Ca

Zn

Sr

Cd

B

Al

*

*

Y

In

C

Si

Ti

*

Zr

Sn

N

P

V

As

Nb

Sb

O

S

Cr

Se

Mo

Te

F

Cl

Mn

Br

*

I

Fe Co Ni

Ru Rh Pd

1

2

3

4

5

Group

I II III IV V VI VII VIIIPeriod

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

-

-

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

1

3

11

19

37

55

87

4

12

20

38

56

88

21

39

57-71

89-103

22

40

72

23

41

73

24

42

74

25

43

75

26

44

76

27

45

77

La Ce Pr Nd Pm Sm Eu57 58 59 60 61 62 63

Ac Th Pa U Np Pu Am89 90 91 92 93 94 95

Ni

Pd

Pt

Cu

Ag

Au

28

46

78

29

47

79

50 51 52 53 54

Ar18

C N O F Ne5 6 7 8 9 10

He2

Gd Tb Dy Ho Er Tm Yb64 65 66 67 68 69 70

Cm Bk Cf Es Fm Md No96 97 98 99 100 101 102

Lu71

Lr103

B

Zn

Cd

Hg

Ga

In

Tl

Ge

Sn

Pb

As

Sb

Bi

Se

Te

Po

Br

I

At

Kr

Xe

Rn

30

48

80

31

49

81

32

82

33

83

34

84

35

85

36

86

Al Si P S Cl13 14 15 16 17

Rf104

Db105

Sg106

Bh107

Hs108

Mt109

Rg111

Ds110 112 113 114 115 116

Uub Uut Uuq Uup Uuh


First ionization energy The first ionization energy of an

element is the energy needed toremove a single electron from 1 moleof atoms of the element in the gaseousstate, in order to form 1 mole ofpositively charged ions.

Reading down group 1, there is adecrease in the first ionizationenergies. This can be explained byconsidering the electronicconfiguration of the elements in thegroup. Reading down, the outerelectron is further from the positivelycharged nucleus, and there is anincreasing number of complete shellsof inner electrons, which to someextent, shield the outer electron fromthe nucleus. The result is that lessenergy is needed to remove the outerelectron. A similar situation exists inother groups.

Increase in ionizationenergy There is a general increase in the first

ionization energies across a period.This increase is due to electrons at thesame main energy level being attractedby an increasing nuclear charge. Thischarge is caused by the increasingnumber of protons in the nucleus. Theincrease makes it progressively moredifficult to remove an electron; thusmore energy is needed.

The diagram illustrates this principleusing the first six periods minus thelanthanide series.

Elements whose ionizationenergies are the greatest in their periodHe HeliumNe NeonAr ArgonKr KryptonXe XenonRn Radon

First ionization energiesof the elements

electronelementgroup 1ionionization energy

lanthanide seriesmolenucleusperiodshell

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680

760

770

760

840

880

870

890

1010

590

720

700

810

660

660

680

700

710

720

80

073

0870

560

710

830

870

1010

1170

ZrN

bM

oTc

Ru

Rh

PdA

gC

dIn

SnSb

TeI

Xe

Hf

TaW

Re

Os

IrP

tA

uH

gTl

Pb

Bi

PoA

tR

n38

050

0

40

055

0620

Rb

SrY

Cs

Ba

660

650

650

720

760

760

740

750

910

580

760

950

940

1140

1350

TiV

Cr

Mn

FeC

oN

iC

uZn

Ga

Ge

As

SeB

rK

r420

590

630

KC

aSc

80

010

90

140

013

1016

80

20

80

BC

NO

FN

e

500

740

Na

Mg

520

90

0Li

Be

580

790

1010

100

012

5015

20

Al

SiP

SC

lA

r

2370He

1310H

1 5 6432

La 540

Variation of firstionization energy


First ionization energies The graph shows a repeating pattern,

or periodicity, corresponding toreading down the periods of theperiodic table.

Within a period, it becomesincreasingly more difficult to removean electron due to the increasingnuclear charge. The graph peaks at thelast element in each period, which is anoble gas (labeled on the graph).

The noble gases have complete outershells of electrons. This electronconfiguration provides great stability,and consequently, the noble gases arevery unreactive. Some are totallyunreactive. The first ionizationenergies of the noble gases are veryhigh.

ionization energynoble gasesperiodperiodicityshell

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Firs

tio

niza

tion

ener

gy/K

Jm

ol–1

2,000

90Atomic number

2,500

1,500

1,000

500

00 8070605040302010

a = 2,370

b = 2,080

d = 1,350

c = 1,500

e = 1,170

f

a Heliumb Neonc Argon

d Kryptone Xenonf Radon

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Melting points The melting point is the point at

which the solid and liquid phase of asubstance is in equilibrium at a givenpressure.

In a solid, the particles are held in arigid structure by the strong forces ofattraction that exist between them.They vibrate but cannot moveposition. When a solid is heated to itsmelting point, the particles gainsufficient energy to overcome theseforces of attraction, and the particlesare able to move position.

Within groups of metallic elements,the melting point decreases down thegroup. The converse is true for non-metals, where the melting pointincreases down the group.

Reading across periods 2 and 3, theelements follow a pattern of metallicstructure, giant covalent structure, andsimple covalent structure. The meltingpoint increases until a maximum isreached with the element that exists asa giant covalent structure.

The more reactive metals in group 1are soft and have low melting points.Transition metals (elements that havean incomplete inner electronstructure) are generally harder andhave higher melting points.

The noble gases exist as single atomswith only weak forces of attractionbetween them. Consequently, theirmelting points are very low.

Using the first six periods minus thelanthanide series, the diagramhighlights the element with thehighest melting point in a period.

Elements whose melting pointsare the greatest in their periodC CarbonSi SiliconV VanadiumMo MolybdenumW Tungsten

Melting points of theelements °C

groupgroup 1lanthanide seriesliquidmelting point

noble gases periodsolidtransition metals

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2227

2996

3410

3180

270

024

1017

7210

64

–39

304

328

271

254

304

–71

1852

2467

2610

217

223

1019

66

1554

962

321

156

232

631

450

114

–112

ZrN

bM

oTc

Ru

Rh

PdA

gC

dIn

SnSb

TeI

Xe

Hf

TaW

Re

Os

IrP

tA

uH

gTl

Pb

Bi

PoA

tR

n29

725

3976

915

22R

bSr

Y

Cs

Ba

1660

1890

1857

1244

1535

1495

1455

1083

420

30937

817

217

–7–1

57Ti

VC

rM

nFe

Co

Ni

Cu

ZnG

aG

eA

sSe

Br

Kr

63

839

1541

KC

aSc

230

037

00

–270

–218

–220

–248

BC

NO

FN

e

98

649

Na

Mg

181

1278

LiB

e

660

1410

44

119

–10

1–1

89

Al

SiP

SC

lA

r

–270He

–259H

1 5 6432

La 921

Variation of meltingpoints


Melting points The graph shows a repeating pattern,

or periodicity, corresponding toreading down the periods of theperiodic table.

The structure of periods 2 and 3 with regard to the nature of theelements, is:Elements having a metallic structure:melting point increasingElements having a giant covalentstructure: melting point maximumElements having a simple covalentstructure: melting point decreasing

In general, the melting point increasesat the start of these periods,corresponding to elements that havemetallic structure. The melting point isat maximum for elements that have agiant covalent structure (labeled onthe graph). After this, the meltingpoint rapidly falls to low values,corresponding to those elements thathave a simple covalent structure.

elementmelting pointperiodperiodicityperiodic table

Key words

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Mel

ting

poin

t°C

2,500

90Atomic number

2,000

1,000

500

0

0 8070605040302010

a

b

d

c

e

1,500

3,000

a Carbonb Siliconc Vanadiumd Molybdenume Tungsten©

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Boiling points The boiling point is the temperature

at which a liquid becomes a gas. The particles in a liquid are held

together by the strong forces ofattraction that exist between them.The particles vibrate and are able tomove around, but they are held closelytogether. When a liquid is heated to itsboiling point, the particles gain kineticenergy, moving faster and faster.Eventually, they gain sufficient energyto break away from each other andexist separately. There is a largeincrease in the volume of anysubstance going from a liquid to a gas.

Within groups of metallic elements,the boiling point decreases down thegroup. The converse is true for non-metals: the melting point increasesdown the group.

The more reactive metals in group 1have relatively low boiling points.Transition metals generally have veryhigh boiling points.

The noble gases exist as single atomswith only weak forces of attractionbetween them. Consequently, theirboiling points are very low because ittakes relatively little energy toovercome these forces.

Using the first six periods minus thelanthanide series, the diagramhighlights the element with thehighest boiling point in a period.

Elements whose boiling pointsare the greatest in their periodC CarbonSi SiliconV VanadiumMo MolybdenumRe Rhenium

Boiling points of theelements °C

boiling pointgasgroupgroup 1kinetic energy

lanthanide seriesliquidnoble gasestransition metals

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460

254

2754

20

5627

5297

413

038

2730

80

357

1457

1740

1560

962

337

–62

437

7474

255

60

4877

390

037

2729

7022

1276

520

80

2260

1750

990

184

ZrN

bM

oTc

Ru

Rh

PdA

gC

dIn

SnSb

TeI

Xe

Hf

TaW

Re

Os

IrP

tA

uH

gTl

Pb

Bi

PoA

tR

n669

1640

686

1384

3338

Rb

SrY

Cs

Ba

3287

3380

2670

1962

2750

2870

2730

2567

90

724

03

2830

613

685

59–1

52Ti

VC

rM

nFe

Co

Ni

Cu

ZnG

aG

eA

sSe

Br

Kr

760

1484

2831

KC

aSc

2550

4827

–196

–183

–188

–246

BC

NO

FN

e

883

110

7N

aM

g

1342

2970

LiB

e

2467

2620

280

445

–35

–186

Al

SiP

SC

lA

r

–269

He

–253H

1 5 6432

La 3457

Variation of boilingpoints


Variation of boiling point The majority of non-metallic elements

are gases at room temperature andatmospheric pressure. Most non-metallic elements have simple covalentstructures and have very low boilingpoints.

Elements with metallic and giantcovalent structures have very highboiling points (see diagram). Theboiling points of transition metals aregenerally much higher than those ofthe group 1 and group 2 metals.

boiling pointgasgroup 1group 2transition metals

Key words

32

Boi

ling

poin

t°C

2,500

90Atomic number

2,000

1,000

500

0

0 8070605040302010

a

b

dc e

1,500

3,000

a Carbonb Siliconc Vanadiumd Molybdenume Rhenium©

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Atomic volume The atomic volume is the volume of

one mole of the atoms of an element.It can be found by dividing the atomicmass of one mole of atoms by thedensity of the element:Atomic volume = Atomic mass

Density

Since there are 6.023 x 1023 atoms permole of atoms, it would seem possibleto use the atomic volume to calculatethe volume of a single atom, and thusits radius. However there are twoproblems with doing this. First, thestate of an element, and therefore itsdensity, changes with temperature andpressure. Second, using the atomicvolume to calculate the volume of asingle atom assumes that an elementconsists of atoms that are not bondedto each other. This is true only of thegroup 8 elements (noble gases). Forthese reasons, it is not possible toconsider the volume of an atom inisolation, but only as part of thestructure of an element.

In general, atomic volume increasesdown a group. Across a period, itdecreases and then increases.

The diagram highlights the elementwith the highest atomic volume in thefirst six periods (minus the lanthanideseries).

Elements with peak atomicvolumesHe HeliumK PotassiumRb RubidiumCs CesiumRn Radon

Atomic volumes of theelements

atomic massatomic volumedensityelementgroup

group 8lanthanide seriesmolenoble gasesperiod

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13.5

10.9

9.6

8.9

8.5

8.6

9.1

10.2

14.8

17.2

18.3

21.

450

.5

14.2

10.9

9.4

8.1

8.3

8.8

10.3

13.0

15.8

16.4

18.2

20

.425

.642.9

ZrN

bM

oTc

Ru

Rh

PdA

gC

dIn

SnSb

TeI

Xe

Hf

TaW

Re

Os

IrP

tA

uH

gTl

Pb

Bi

PoA

tR

n71

.039

.2

55.7

34.0

16.1

Rb

SrY

Cs

Ba

10.6

8.9

7.3

7.4

7.1

6.6

6.6

7.1

9.2

11.8

13.3

13.1

16.5

25.6

32.2

TiV

Cr

Mn

FeC

oN

iC

uZn

Ga

Ge

As

SeB

rK

r44.9

26.0

14.7

KC

aSc

4.3

5.4

17.3

14.0

17.1

16.8

BC

NO

FN

e

23.7

14.0

Na

Mg

13.0

4.9

LiB

e

10.0

11.6

16.9

15.5

18.7

24.2

Al

SiP

SC

lA

r

31.8

He

14.1H

1 5 6432

La 22.6

8.5

22.2

3

Variation of atomicvolumes


Periodicity As early as the Middle Ages, scientists

recognized that elements could bedifferentiated by their properties andthat these physical and chemicalproperties were periodic.

The German chemist Lothar Meyerdemonstrated periodicity by plottingatomic volumes against atomicweights (the term atomic mass is nowused).

This periodicity is better shown byplotting atomic volumes againstatomic number.

You can see periodicity most clearly bythe pattern between potassium (b)and rubidium (c), and betweenrubidium (c) and cesium (d) in thediagram. These correspond to thechanging values across period 4 andperiod 5, respectively.

atomic massatomic number atomic volumeperiodicity

Key words

34

Ato

mic

volu

me

cm3 m

ol–1

60

90Atomic number

50

30

20

00 8070605040302010

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b

d

c

e

40

70

10

a Heliumb Potassiumc Rubidiumd Cesiume Radon©

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1 Carbon-12 To compare the masses of different

atoms accurately, scientists need astandard mass against which all othermasses can be calculated. Masses aregiven relative to this standard.

The isotope carbon-12 is used as thestandard. On this scale, atoms ofcarbon-12 are given a mass of exactly12. The atomic masses of all otheratoms are given relative to thisstandard.

If an element contained only oneisotope, its atomic mass would be therelative mass of that isotope. However,most elements contain a mixture ofseveral isotopes in varyingproportions.

Natural abundance gives theproportion of each isotope in a sampleof the element.

If more than one isotope of anelement is present, the atomic mass iscalculated by taking an average thattakes into account the relativeproportion of each isotope. Diagrams2 and 3 illustrate how the atomic massof common isotopes of lithium andchlorine would be calculated.

2 Lithium There are two common isotopes of

lithium: lithium-6 and lithium-7. The atomic mass of lithium is 6.925,

but for most calculates a value of 7 issufficiently accurate.

3 Chlorine There are also two common isotopes

of chlorine: chlorine-35 and chlorine-37.

The atomic mass of chlorine is35.4846, but for most calculations avalue of 35.5 is sufficiently accurate.

Rounding the atomic mass of chlorineto the nearest whole number wouldlead to significant errors incalculations.

Atomic massatomic massisotope

Key words

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The relative atomic mass of lithium is given by:

(6 × 7.5) + (7 × 92.5) = 6.925 100

The relative atomic mass of lithiumis given by:

(35 × 75.77) + (37 × 24.23) = 35.4846 100

+

++

+

+

+

1 Carbon-12

Isotope Natural abundance

Lithium-6

Lithium-7 92.5%

7.5%

2 Lithium

Isotope Natural abundance

Chlorine-35

Chlorine-37 24.23%

75.77%

3 Chlorine

( Li)63

( Li)73

( Cl)3517

( Cl)3717

( C)126

Periodic table withmasses and numbers


Atomic mass The atomic mass of an element is the

average of the relative masses of itsisotopes. It provides the relative massof an “average” atom of the element,which is useful for calculations.

The atomic mass is represented by thesymbol A(r)

The atomic mass of an isotope is itsmass relative to the isotope carbon-12.

The atomic mass of an isotope is thesum of the protons and neutrons in itsnucleus.

The atomic masses of the elements arepresented below the element on theperiodic table at right.

Atomic number The atomic number of an element is

the number of protons in its nucleus. The atomic number is usually

represented by Z. The number of neutrons in the

nucleus of an isotope is:A(r) – Z

The atomic numbers of the elementsare presented above the element inthe periodic table at right.

atomic massatomic numberelementisotope

Key words

36

H Li Na K Rb Cs Fr

Be

Mg

Ca

Sr

Ba Ra

Sc Y

Ti Zr

Hf

V Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe Ru

Os

Co

Rh Ir

1 3 11 19 37 55 87

4 12 20

38 56 88

21

39

22

40

57–7

1

23

41

73

24

42 74

25

43

75

26

44

76

27

45

77

LaC

eP

rN

dP

mS

mEu

5758

5960

61

62

63

Ni

Pd Pt

Cu

Ag

Au

28

46

78

29

47

79

5051

5253

54Ar

18

CN

OF

Ne

56

78

910He2

Gd

Tb

Dy

Ho

Er

Tm

Yb

64

65

66

67

68

69

70

Lu71

B

Zn

Cd

Hg

Ga In Tl

Ge

Sn

Pb

As

Sb Bi

Se Te

Po

Br I At

Kr

Xe

Rn

30 48

80

31 49

81

32 82

33 83

34 84

35 85

36 86

Al

Si

PS

Cl

1314

1516

17

89–1

03

Ac

Th

Pa

UN

pP

uA

m89

90

91

92

93

94

95

Cm

Bk

Cf

Es

FmM

dN

o96

97

98

99

100

101

102

Lr103

6.9

4

1.0

08

9.0

110

.81

12.0

1

4.0

0

14.0

116

.00

19.0

020

.18

23.

00

24.3

127.

00

28.0

830

.97

32.0

635

.45

39.9

5

39.1

040

.08

69.7

272

.64

74.9

278

.96

79.9

083.

80

54.9

455

.84

58.9

358

.69

63.

5565.

41

44.9

647.

87

50.9

452

.00

85.

47

87.

62

114.8

211

8.7

112

1.76

127.

60

126.9

013

1.29

98.0

010

1.0

710

2.9

010

6.4

210

6.9

011

2.4

188.9

091.

22

92.9

195.

94

132.9

013

7.33

20

4.3

820

7.20

20

8.9

8210

210

220

186.2

119

0.2

319

2.2

219

5.0

819

6.9

720

0.5

917

8.4

918

0.9

518

3.84

223

226

162.5

016

4.9

316

7.26

168.9

317

3.0

417

4.9

714

4.2

414

5.0

015

0.3

615

1.96

157.

25

158.9

213

8.9

014

0.1

214

0.9

1

251

252

257

258

259

262

238

.03

237

244

243

247

247

227

232

.04

231

.03

72 Rf

261

104

Db

105

262

Sg

106

266

Bh

107

264

Hs

108

277

Mt

109

268

Ds

110

271

Rg

111

Uub

Uut

Uuq

Uup

Uuh

112

113

114

115

116

284

289

288

292

272

285

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Calculating molecular massYou calculate the molecular mass of acompound the same way regardless ofstructure: 1. Multiply the number of atoms in anelement by its atomic mass.2. Repeat this process for each elementin the compound, then 3. Add the numbers.

1 Diatonic molecule(chlorine) The element chlorine exists as a

diatomic molecule Cl2.Atomic mass of chlorine = 35.5

Molecular mass of chlorine = 2 x 35.5 = 71

2 Covalent compound(ethanol) Ethanol is a simple covalent

compound that has the formulaC2H5OH.Atomic mass of carbon = 12;hydrogen = 1; oxygen = 16.Molecular mass of ethanol = (2 x 12) + (6 x 1) + (1 x 16) = 46

3 Ionic compound (sodiumchloride) Ionic compounds do not exist as

molecules but as a giant latticecomposed of ions in a fixed ratio. Theformula mass of an ionic compound isthe sum of the atomic masses of theions in their simplest ratio.

Sodium chloride consists of an ioniclattice in which the ions are present inthe ratio 1:1. Therefore, the formula ofsodium chloride is taken to be NaCl.Atomic mass of sodium = 23;chlorine = 35.5.Formula mass of sodium chloride = 23 + 35.5 = 58.5

Calculating the molecularmass of compounds

atomic masscovalent

compounddiatomic

molecule

ionic compoundlatticemolecular mass

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1 Diatomic molecule (chlorine)

3 Ionic compound (sodium chloride)

Cl = 35.45

chlorine

sodium

H = 1C = 12O = 16

Na = 23.00

2 Covalent compound (ethanol)

hydrogen

carbon

oxygen

chlorine

Cl = 35.45

Structure of some ioniccrystals


Ionic crystals In an ionic crystal, each ion is

surrounded by a number of oppositelycharged ions in a lattice structure.

There are several types of ionicstructures. Simple: The atoms form grids.Body centered: One atom sits in thecenter of each cube. Face centered: One atom sits in each“face” of the cube.

The lattice structure is determined bytwo factors:1. the ratio of the number of cations(positively charged ions) to anions(negatively charged ions)2. the ratio of the radii of the ions.

In general, the higher the value of theradius ratio the higher thecoordination number of the lattice.The coordination number is thenumber of atoms, ions, or moleculesto which bonds can be formed.

1 Simple cubic structure(CsCl) In cesium chloride, the radius ratio is

0.94 (due to the large cesium ion).The coordination is 8:8. Each ion issurrounded by 8 oppositely chargedions.

2 Face-centered cubicstructure (NaCl) The radius ratio in the sodium

chloride lattice is 0.57. Thecoordination is 6:6. Each ion issurrounded by 6 oppositely chargedions.

3 Body-centered cubicstructure (CaF2) In calcium fluoride the radius ratio is

0.75. The coordination is 8:4. Eachcalcium ion is surrounded by 8fluoride ions, while each fluoride ion issurrounded by 4 calcium ions.

anionbondcation coordination

number

ionic crystalionlattice

Key words

38

cations

anions

cations

anions

cations

anions

2 Face-centered cubic structure (NaCl)

1 Simple cubic structure (CsCl)

3 Body-centered cubic structure (CaF2)

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ELEMENTS AND COMPOUNDSCrystal structure ofmetals: lattice structure

body centeredcubic packing

crystal face-centered

cubic closepacking

hexagonal closepacking

latticeunit cell

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Metallic crystals Like all other crystals, metallic crystals

are composed of unit cells, sets ofatoms, ions, or molecules in orderlythree dimensional arrangements calledlattices.

1 Hexagonal close packing When arranged in a single layer, the

most efficient method of packing theions is in the form of a hexagon inwhich each ion is surrounded by sixother ions.

In hexagonal close packing, a secondlayer is positioned so that each ion inthe second layer is in contact withthree ions in the first layer. The thirdlayer is placed directly above the first,and the fourth layer directly above thesecond, etc. This arrangement issometimes represented as ABABAB.

2 Face-centered cubicclose packing Here the third layer does not sit

directly above either the first orsecond layers. The pattern is repeatedafter three layers, giving rise to anABCABCABC arrangement.

3 Body-centered cubicpacking Here the layers are formed from ions

arranged in squares. The second layeris positioned so that each sphere inthe second layer is in contact with fourspheres in the first layer. The thirdlayer sits directly above the first layer,giving rise to an ABABAB arrangement.

2 Face-centered cubic close packing

1 Hexagonal close packing

3 Body-centered cubic packing

Crystal structure ofmetals: efficient packing


body-centeredcubic packing

coordinationnumber

face-centeredcubic closepacking

hexagonal closepacking

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Face-centered cubic close packing

1 Efficient packingHexagonal close packing

2 Less efficient packingBody-centered cubic packing

1 Efficient packing Both hexagonal close packing and

face-centered cubic close packing maybe considered as efficient packingsince the spheres occupy 74 percentof the available space. In botharrangements, each sphere is incontact with 12 others, and is said tohave a coordination number of 12.

2 Less efficient packing Body-centered cubic packing is less

efficient than hexagonal and face-centered cubic close packing. Spheresoccupy only 68 percent of the availablespace. Each sphere is in contact witheight others (four in the layer aboveand four in the layer below) and,therefore, has a coordination numberof eight.

Metals showing hexagonalclose packing Cobalt Magnesium Titanium Zinc

Metals showing face-centered cubic closepacking Aluminum Calcium Copper Lead Nickel

Metals showing body-centered cubic packing Group 1 metals Barium Chromium Iron Vanadium


Ionic bonding Ionic bonds are formed by the

attraction of opposite charges. In ionic bonding, the atoms in a

compound gain, lose, or shareelectrons so the number of electronsin their outer shell is the same as thenearest noble gas on the periodictable.

Non-metals gain electrons to givenegatively charged ions (anions).

Metal atoms loose electrons to givepositively charged ions (cations).

1 Formation of sodiumchloride (NaCl) A sodium atom has one electron in its

outer shell. The easiest way it canattain a complete outer shell is bylosing this electron to form a sodiumion, Na+.

A chlorine atom has seven electronsin its outer shell. The easiest way it

can attain a complete outer shell isby gaining one more electron toform a chloride ion, Cl-.

2 Formation ofmagnesium oxide

(MgO) A magnesium atom has two

electrons in its outer shell. It losesthese electrons to form amagnesium ion, Mg2+.

An oxygen atom has six electrons in itsouter shell. It gains two electrons toform an oxide ion, O2-.

Chemical combination:ionic bonding

anionbondcationchlorideionic bonding

noble gasesoxideshell

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Electronic configurationNa (sodium atom) 2.8.1

Na+ (sodium ion) 2.8

Cl (chlorine atom) 2.8.7

Cl- (chloride ion) 2.8.8

Mg (magnesium atom) 2.8.2

Mg2+ (magnesium ion) 2.8

O (oxygen atom) 2.6

O2- (oxide ion) 2.8

1 Formation of sodium chloride (NaCl)

Chlorine atom (Cl)Sodium atom (Na)

Chlorine ion (Cl–) Sodium ion (Na+)

Na Cl Cl–Na+

Sodium chloride(NaCl)

Oxygen ion (O2–)Magnesium ion (Mg2+)

O2–OMg

Magnesium oxide

2 Formation of magnesium oxide (MgO)

Chemical combination:ionic radicals


Radicals A radical is a group of atoms that

cannot be represented by onestructural formula. It can passunchanged through a series ofchemical reactions. Radicals includethe carbonate ion, CO3

2-, the nitrateion, NO3

-, and the sulfate ion, SO42-.

1 Carbonate ion The carbon atom is bonded to three

oxygen atoms. By transferringelectrons, it is possible to write threelimiting forms for this ion. (Limitingforms are the possibilities for thedistribution of electrons in a moleculeor ion.)

Electrons are continually beingtransferred in the ion. Thus its exactform is constantly changing. The ion isbest represented as a resonancestructure (the average of the limitingforms) in which dotted lines indicatethat the charge on the ion, 2-, isspread over all three of thecarbon–oxygen bonds.

2 Nitrate ion The nitrogen atom is bonded to three

oxygen atoms. This ion has threelimiting forms.

It is best represented as a resonancestructure in which dotted linesindicate that the charge on the ion, 1-,is spread over all three of thenitrogen–oxygen bonds.

3 Sulfate ion The sulfur atom is bonded to four

oxygen atoms. This ion has threelimiting forms.

The ion’s exact form is constantlychanging. It is best represented as aresonance structure in which dottedlines indicate that the charge on theion, 2-, is spread over all four of thesulfur–oxygen bonds.

carbonateionlimiting formnitrateradical

resonancestructure

sulfate

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O C

O

O

O C

O

O

–

––

O C

O

O

–

–O C

O

O

2–

1 Carbonate ion

limitingforms

resonancestructure

O N

O

O

O N

O

O–

–O N

O

O

–

O N

O

O

–

2 Nitrate ion

limitingforms

resonancestructure

S

O

O

– 2–

3 Sulfate ion

limitingforms

resonancestructure

O

O

–

S

O

O

–O

O–

S

O

O–

O

O–

S

O

O

–O

O

S

O

O

O

O


Covalent bonding Atoms gain stability by having a

complete outer shell of electrons. Inionic compounds, this is achieved bythe transfer of electrons. In covalentbonding, atoms share electrons.

1 The hydrogen molecule A hydrogen atom has one electron in

its outer shell. In a hydrogenmolecule, two hydrogen atoms eachdonate this electron to form a bond.Each hydrogen atom can be thoughtof as having control of the pair ofelectrons in the bond. Thus, each canbe thought of as having a full outershell of electrons. The single bond isshown as H-H.

2 The ammonia molecule A nitrogen atom has five electrons in

its outer shell and needs another threeelectrons to complete the shell. Inammonia, three hydrogen atoms eachdonate one electron to form three N-Hbonds. The nitrogen atom now hascontrol of eight electrons and has acomplete outer shell, while eachhydrogen atom has control of twoelectrons and also has a completeouter shell.

3 The methane molecule A carbon atom has four electrons in

its outer shell and needs another fourelectrons to complete the shell. Inmethane, four hydrogen atoms eachdonate one electron to form four C-Hbonds. The carbon atom now hascontrol of eight electrons and has acomplete outer shell, while eachhydrogen atom has control of twoelectrons and also has a completeouter shell.

Chemical combination:covalent bonding

ammoniabondcarbonhydrogenionic compound

methanenitrogenshell

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nitrogenatom

3 hydrogenatoms

ammoniamolecule (NH3)

amolecule (CH4)4 hydrogenatoms

carbon atom

2 hydrogenatoms

hydrogenmolecule (H2)

1 The hydrogen molecule

4 The methane molecule

3 The ammonia molecule

Chemical combination:coordinate bonding


Coordinate bonding Coordinate bonding is a particular

form of covalent bonding in which oneatom provides both electrons that thetwo atoms share.

1 Ammonium ion There is a non-bonding or lone pair of

electrons on the nitrogen atom of anammonia molecule. Nitrogen uses thislone pair to form a coordinate bondwith a hydrogen ion, forming theammonium ion, NH4

+.

2 Hydronium ion The hydronium ion, H3O+, forms in a

similar way.

3 Aluminum chloride The Al3+ ion is very small and carries a

high charge. It attracts electrons sostrongly that aluminum chloride is acovalent compound. It exists as Al2Cl6molecules in which two AlCl3molecules are linked by coordinatebonds formed by the donation of lonepairs of electrons from two chlorineatoms.

4 Ionic compounds withcovalent character The ions in a sodium chloride lattice

are perfectly spherical. Thus the bondsin this compound are said to beperfectly ionic.

But in an ionic compound consistingof a small, highly charged positive ionand a large negative ion such aslithium iodide, the positive ion attractselectron charge away from thenegative ion. The result is that thenegative ion becomes distorted, andelectron density becomesconcentrated between the ions,creating a bond similar to a covalentbond. Compounds like lithium iodideare said to be ionic with covalentcharacter.

ammonium ioncoordinate

bondingcovalent bond

covalentcompound

hydronium ionlone pair

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+

••

••

••

H

1 Ammonium ion

2 Hydronium ion

4 Ionic compounds with covalent character

N

H

H

H

N

H H+

H

H

H

O

H

H

O

H H+ H

Cl

Al

Cl Cl

Cl

Al

Cl

Cl

3 Aluminum chloride

+

••

Na+ Cl– Li+ I–

CHANGES IN MATTER

45

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Mixtures and solutions

1 Solutions A solution is a homogeneous mixture

of substances. Particles in solutions arevery small and cannot be seen. Theparticles may be atoms, ions, ormolecules, and their diameters aretypically less than 5 nm. Salt dissolvesin water to form a clear colorlesssolution.

Many, but not, all ionic compoundsare soluble in water.

A small proportion of organiccompounds are soluble in water.However, organic compounds aregenerally more soluble in organicsolvents such as hexane and ethanol.

2 Suspensions A suspension is a heterogeneous

mixture of two components. Theparticles will settle out over a period oftime. Suspended particles havediameters that are typically 1,000 nmor more.

When flour is mixed with water, itforms a white suspension. Tinyparticles of flour are suspended in thewater. The flour particles can befiltered off from the suspension.

3 Emulsions An emulsion is a colloidal dispersion

of small droplets of one liquid inanother (See page 46).

When oil and water are mixed, theyform an emulsion. Oil is less densethan water and forms the upper layer.

Tiny oil droplets are suspended in thewater. After a while, the oil dropletsjoin together, and two layers areformed.

The mixture of oil and water can beseparated using a separating funnel.

emulsionionic compoundmixturesolublesolution

suspension

Key words

water flour cloudy mixture with solidparticles in the liquid

Producing a suspension

water salt clear liquid

Producing a solution

water cloudy mixtureforming an emulsion

when shaken

liquids separatewhen left to stand

oil

Producing an emulsion

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ColloidsCHANGES IN MATTER

Colloids A colloid is a substance made of

particles whose size is intermediatebetween those in solutions andsuspensions.

The particles in a suspension have adiameter of typically 1,000 nm ormore. The particles in a suspensionwill settle over a period of time.

The particles in a colloid areapproximately 500 nm or less indiameter and do not settle onstanding.

The particles in a colloid cannot beseparated from the dispersion mediumby ordinary techniques like filtrationand centrifugation.

A colloid consists of a dispersingmedium and dispersed substance.These terms are analogous to theterms solute and solvent.

Colloids are classified according to theoriginal phases of their constituents.The main types are: aerosols, foams,emulsions, sols, and gels.

Aerosols are extremely small solid orliquid particles suspended in air oranother gas.

Foams form when a gas is suspendedin a liquid or a solid.

Emulsions form when small particlesof a liquid are suspended in anotherliquid.

Sols form when solid particles aresuspended in a liquid.

Gels are solid particles arranged as afine network in a liquid to form a jelly.

46

aerosolcolloidemulsionfiltration foam

gelsolsolutionsuspension

Key words

solid

solid

solid

gas

liquid

solid

solid foam

gel

solid sol

cork, polyurethane

agar, geletine, jelly

alloys

2 Phase ofdispersing medium

3 Phase ofdispersed substance

1 Colloid type Examples

liquid

liquid

liquid

gas

liquid

solid

foam

emulsion

sol

froth, whipped cream

milk, salad dressing

milk of magnesia, paint




gas

gas

liquid

solid

aerosol

aerosol

clouds, fog, insecticide spray

dust, smoke




3 In solids

2 In liquids

1 In Air

aerosol

paint

polystyrenecork

CHANGES IN MATTER

47

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1 Simple distillation Distillation is a process in which a

mixture of materials is heated toseparate the components.

Simple distillation is used when theboiling points of the components arewidely separated.

In the diagram, salt water is placed in around-bottom flask. Water boils at100°C and becomes water vapor.

A condenser consists of an inner tubesurrounded by a jacket of cold water.This jacket ensures that the inner tuberemains cool.

The vapor passes into the condenser,where it is cooled and changes backinto liquid.

The water runs out of the condenserand is collected in a second flask.

The salt remains in the round-bottomed flask.

2 Fractional distillation Fractional distillation is used to

separate components whose boilingpoints are similar.

Ethanol boils at 78°C and turns tovapor. Because the boiling point ofwater is only 100°C, a significantamount of water also becomes vaporas a result of evaporation.

The fractionating column containsglass beads, which provide a largesurface area for vapor to condense andthe resulting liquid to subsequentlyboil.

As the vapor mixture moves up thefractionating column, it condenses andthen boils again to become vapor.Each time, the proportion of ethanolin the mixture increases.

boiling pointdistillationfractional

distillationmixture

Key words

Simple distillation of sea water

Fractional distillation of ethanol

a sea waterb heat sourcec thermometerd condenser with cold watere cold water inf cold water outg distillate of pure waterh solution of alcohol and wateri fractionating column of glass beadsj distillate of ethanol

a

b

c

d

g

h

j

f

e

i

b

c

f

d e

78°C

79°C

80°C

boiling point (°C)

salt

water

1,420

100

boiling point (°C)

ethanol

water

78

100

Simple and fractionaldistillation

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Separating solutionsCHANGES IN MATTER

1 Separating a mixture oftwo solids Sugar is soluble in ethanol, while salt is

insoluble. When a mixture of sugarand salt is mixed with ethanol, thesugar dissolves while the salt does not.

When the mixture is filtered, theundissolved salt remains as the residuein the filter. The filtrate, sugarsolution, passes through the filter.

If the filtrate is left open to the air, theethanol evaporates, and solid sugarremains.

2 Separating two solutes insolution Salt dissolves in water but not in

carbon tetrachloride. Iodine is slightly soluble in water but is

far more soluble in carbontetrachloride.

When a mixture of salt and iodine isshaken in a mixture of water andcarbon tetrachloride, the salt dissolvesin the water and the iodine in carbontetrachloride.

Water and carbon tetrachloride areimmiscible, they do not mix, and formtwo layers in a separating funnel.Carbon tetrachloride is more densethan water and forms the lower layer.

When the layers are run into separateevaporating basins and left, thesolvents—carbon tetrachloride andwater—evaporate, leaving salt andiodine respectively.

48

filtrateimmiscibleinsolublemixtureresidue

solublesolvent

Key words1 Separating a mixture of two solids

Salt and sugarmixture

Ethanol is added tomixture — sugar dissolves

but not salt

The solution isfiltered

The ethanol evaporatesleaving solid sugar

Carbon tetrachlorideis added

Each of the solvents are evaporatedoff to obtain the two solutes

2 Separating two solutes in solution

Brown solution ofsalt and iodine

The two immiscible solutionsare separated using a

separating funnel

b

c

d

a

c

d

a salt left on filter paperb sugar solution

c salt solution in waterd purple solution of iodine in carbon tetrachloride

CHANGES IN MATTER

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Paper chromatography

1 Paper chromatography Chromatography is a technique for

separating and identifying mixtures ofsolutes in solutions.

In paper chromatography, absorbentpaper is suspended on a support sothat only the bottom rests in thesolvent.

A base line is drawn in pencil abovethe level of the solvent. (If ink wereused, the dyes in the ink wouldseparate during the process and mixwith the sample.)

A concentrated solution of the samplemixture is made by dissolving as muchas possible in a very small volume ofsolvent.

A small amount of the concentratedsolution is spotted onto the base line.The chromatography paper issuspended over the solvent.

The solvent rises up thechromatography paper.

2 Rf value The Rf value is the ratio of the

distance moved by a substance in achromatographic separation to thedistance moved by the solvent. Thegreater the attraction between asubstance and the solvent molecules,the greater the Rf value.

The molecules of each substance in amixture are attracted both to thechromatography paper and to thesolvent molecules.

The greater the attraction between asubstance and the solvent molecules,the quicker it will be carried up thechromatography paper. Dyes that arevery soluble in the solvent are carriedup to the top of the paper, while thosethat are less soluble remain lowerdown.

The Rf value is independent of theheight of the solvent front but isdependent on the solvent used.

chromatographyRf valuemixturesolutesolution

solvent

Key words1 Paper chromatography

2 Rf value

chromatography paper

solvent front

sample

pencil line

solvent

solvent front

support

base line

10cm

7cm

4cm

1cm

Rf = 0.7

Rf = 0.4

Rf = 0.1

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Gas-liquidchromatography andmass spectrometry

CHANGES IN MATTER

1 Gas-liquidchromatography In chromatography, substances are

partitioned between a stationaryphase and a mobile phase. Thestationary phase is the substance thatretards the components of the sample.The mobile phase is the componentsof the sample.

In gas-liquid chromatography, thestationary phase, packed into thecolumn, consists of a high-boilingpoint liquid, such as a long-chainalkane, supported by a porous inertsolid, such as charcoal or silica.

The mobile phase consists of a carriergas—usually nitrogen, hydrogen,helium, or argon.

A sample mixture is injected into thechamber where it vaporizes and iscarried through the column by thecarrier gas. Various compounds in thesample pass through the column atdifferent rates due to their attractionto the stationary phase.

The separated compounds pass to adetector or directly into a massspectrometer.

2 Mass spectrometry Mass spectrometry is a technique used

to identify the chemical constitution ofa substance by means of analyzing itsions.

The sample passes into the ionizationchamber, where it is bombarded byelectrons and forms a series of positiveions.

The ions are accelerated by an electricfield and deflected along a circularpath by a magnetic field. The lighterthe ions, the greater the deflection.

The intensity of the ion beam isdetected electrically, amplified, andfinally recorded.

Each compound gives a characteristicspectrum from which it can beidentified.

50

alkanechromatographygas-liquid

chromatography

massspectrometry

mobile phasestationary phase

Key words

1 Gas-liquid chromatography

2 Mass spectrometry

carriergas

oven

column

injection ofsample

recorder

flow meter

detector

reservoir ionisation chamber

negatively chargedplates

variablemagneticfield

vacuum

heavierparticles

lighterparticles

electrongun

sampleinlet

amplifier

recorder

CHANGES IN MATTER

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The pH scale

1 pH scale pH is a measure of the acidity or

alkalinity of a solution. The term pHwas originally introduced by theDanish biochemist Søren Sørensen in1909 while working on methods ofimproving the quality control of beer.The letters pH stand for “potential ofhydrogen.”

Acidic solutions always have a pH ofless than 7, and alkaline solutionsalways have a pH of more than 7. Thelower the pH value, the more acidicthe solution; conversely, the higherthe pH value, the more alkaline thesolution.

The pH of a solution is the logarithmto base 10 of the reciprocal of thenumerical value of the hydrogen ionconcentration:pH = lg(1/[H+]0 = -lg [H+]

The pH of a neutral solution can becalculated directly from the ionicproduct (Kw) of water:Kw = [H+][OH-] = 10-14 mol2 dm-6

For a neutral solution:[H+] = [OH-] = 10-7 mol dm-3

therefore the pH of a neutral solution= 7.

The pH scale is logarithmic, sohydrogen ion concentration increasesor decreases by a power of 10 for eachstep down or up the scale.

2 pH meter A pH meter is an electrochemical cell

consisting of an electrode, such as aglass electrode, which is sensitive tohydrogen ion concentration, and areference electrode.

The emf (electromotive force) of thecell can be measured using a high-resistance voltmeter. A pH meter is ahigh-resistance voltmeter calibratedwith the pH scale.

acidityalkalinitypHpH meter

Key words

10–14

0

10–1410–1210–1110–1010–910–810–710–610–510–410–310–210–11

1 2 3 4 5 6 7 8 9 10 11 12 13 14

[H+]/mole dm–3

pH

Increasing acidity Increasing alkalinity

Higher pH/sronger alkaliLower pH/sronger acid

Neutral

1 pH scale

2 Schematic of a pH meter

a

b

c

d

g

he

f

a platinum wireb sensitive voltmeterc silver wire coated with silver

chloride (AgCl)d saturated potassium chloride (KCl)

e capillary opening with porous plugf solution of unknown pHg Thin glass membrane through which H+ ions can passh solution of fixed acid pH

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Indicators CHANGES IN MATTER

1 Common indicators Acid-base indicators are substances

that are different colors in acids andalkalis so they “indicate” whether asolution is an acid or alkali.

2 Changing equilibrium Acid-base indicators are usually weak

acids that disassociate to give an ionthat is a different color than the acid. A change in pH causes a change in theposition of the equilibrium of thereaction and, therefore, the color ofthe solution.

Phenolphthalein is such an indicator. Itis a colorless, weak acid thatdissociates in water, forming pinkanions. Under acidic conditions, theequilibrium of the reaction is to theleft, and the concentration of theanions is too low for the color to bevisible. Under alkaline conditions, theequilibrium is to the right, and theconcentration of anions is highenough for the pink to be seen.

3 Universal indicator In contrast to an indicator such as

phenolphthalein, which is able toshow whether a substance is an acid orbase only in the broadest terms, auniversal indicator has a range ofcolors that indicate how acidic or howalkaline a solution is.

4 pH range of indicators Most indicators do not change color

when the pH of a solution is exactly 7.This means that the end point of thetitration, the point at which theindicator undergoes the maximumcolor change, occurs at a differenttime to the equivalence point of thetitration, the point at which there areequivalent amounts of acid and alkali.

The suitability of an indicator for usein a titration depends on whatcombination of strong and weak acidand alkali is to be used.

52

acidacid-base

indicatoralkaliend point

equilibriumtitrationuniversal

indicator

Key words

3 Universal indicator

pH range overwhich color

change occursAcid AlkaliIndicator

Color

bromocresol green

bromothymol blue

methyl orange

methyl red

phenolphthalein

phenol red

yellow

yellow

red

yellow

colorless

yellow

blue

blue

yellow

red

pink

red

3.8–5.4

6.0–7.6

3.2–4.4

4.8–6.0

8.2–10.0

6.8–8.4

4 Table of pH range over which acid–base indicatorschange color

1 Table of common indicators

Indicator Color in acid Color in alkali

litmus red blue

methyl orange red yellow

phenolphthalein colorless pink

red orange yellow green blue purple

0 2 3 4 5 6 7 8 9 10 111 12 13 14

pH

Color

OH

OH

O

C

C

O

+ H2O

colorless(acid)

OH

OH

O–

C

C

O

+ H2O+

pink(base)

2 Changing equilibrium (phenol phthalein)

CHANGES IN MATTER

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Titration of strong acids

1 Titration of strong acidagainst strong alkali At the end point of strong acid–strong

base alkali titration, the pH changesby 5 or 6 pH units when only 1 drop ofacid or alkali is added.

Methyl orange, bromothymol blue,and phenolphthalein are all suitableindicators for this titration becausethey all change color within a verysmall change in volume of sodiumhydroxide solution.

2 Titration of strong acidagainst weak alkali At the end point of a strong acid–weak

alkali titration, the pH change for theaddition of one drop of acid or alkali issignificant. However, the pH atequivalence (when there areequivalent amounts of acid and alkali)is less than 7. A suitable indicatorshould change color below or aroundpH 7. Thus both methyl orange andbromothymol blue would be suitableindicators because they change colorbetween pH 3.2 and 7.6. Within thisrange, the pH of the titration mixturechanges significantly for a very smallchange in volume of sodiumhydroxide solution.

Phenolphthalein would not be a goodchoice of indicator because it changescolor between pH 8.2 and 10.0. Inorder to change the pH of the titrationmixture over this pH range, asignificant volume of sodiumhydroxide solution must be added.The result would be an overestimateof the volume of sodium hydroxidesolution needed to neutralize the acid.

acidalkalibaseend pointpH

titration

Key words1 Titration of strong acid against strong alkali

(pH changes during the titration of 50 cm3 of 0.1M HClwith 0.1M NaOH)

pHnu

mbe

r

4

20

Volume of 0.1 M NaOH added (cm3)

2 Titration of strong acid against weak alkali

(pH changes during the titration of 50 cm3 of 0.1 M HClwith 0.1 M NH3)

bromothymol blue

bromothymol blue

00 10010 30 40 50 60 70 80 90

12

2

6

8

10

pHnu

mbe

r

4

20

Volume of 0.1 M NH3 added (cm3)

00 10010 30 40 50 60 70 80 90

12

2

6

8

10

phenolphthalein

phenolphthalein

methyl orange

methyl orange

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Titration of weak acidsCHANGES IN MATTER

1 Titration of weak acidagainst strong alkali At the end point of a weak

acid–strong alkali titration, the pHchange for the addition of one drop ofacid or alkali is significant. However,the pH at equivalence (when there areequivalent amounts of acid and alkali)is greater than 7. A suitable indicatorshould change color above pH 7. Thusphenolphthalein would be a goodchoice because it changes colorbetween pH 8.2 and 10.0. Within thisrange, the pH of the titration mixturechanges significantly for a very smallchange in volume of sodiumhydroxide solution.

Conversely, bromothymol blue andmethyl orange would not be goodchoices because they change colorbetween pH 3.2 and 7.6, which isbefore the equivalence point of thetitration is reached. The result wouldbe an underestimate of the volume ofsodium hydroxide solution needed toneutralize the acid.

2 Titration of weak acidagainst weak alkali The pH changes too slowly around the

equivalence point to give a colorchange with the addition of one dropof acid or alkali. The use of methylorange, bromothymol blue, orphenolphthalein would not giveaccurate results.

It is not usual to titrate weak acidswith weak alkali, but if it must bedone, a pH meter is necessary to findthe equivalence point accurately.There is no suitable indicator for thistype of titration.

54

acidalkaliend pointequivalence pointpH

titration

Key words

phenolphthalein

bromothymol blue

methyl orange

phenolphthalein

bromothymol blue

methyl orange

14

7

0

14

7

0

1 Titration of weak acid against strong alkali

Volume of base

pH

2 Titration of weak acid against weak alkali

Volume of base

pH

CHANGES IN MATTER

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pH and soil

1 Soil classification Soil can be classified according to its

pH. Soils naturally tend to become more

acidic due to organic acids beingreleased into the soil as a result of thedecay of organic material.

The acidity of soil can be reduced byspreading slaked lime (calciumhydroxide) or lime (calciumcarbonate).

2 pH range of commonfruits and vegetables Most plants grow best in soil that is

slightly acidic, with a pH valuebetween 6.3 and 7.2. Plants will growoutside this range but not as well. Thishas serious implications for foodcrops.

The soil pH is an importantconsideration in preparing soil to growcrops.

3 Elements needed byplants Plants need a number of major and

minor elements in order to grow well,and they obtain these from the soil.The minerals dissolve in soil water andare absorbed into the plant throughthe roots.

The pH of the soil determines howeasily minerals containing theseelements can be absorbed. At soil pHvalues between 6.0 and 7.0, all majorelements and minor elements can beabsorbed, although some are absorbedmore easily than others. In very acidicor very alkaline soils, relatively fewplants prosper because they cannotabsorb all of the minerals needed forhealthy growth.

pH

Key words1 Soil classification

2 pH range of common fruit and vegetables

3 Elements needed by plants

pH

Fruit or vegetable

Description

Soil pH range

< 5.5

5.5 – 5.9

6.0 – 6.4

6.4 – 6.9

7.0

7.1 – 7.5

7.6 – 8.0

8.1 – 8.5

> 8.5

strongly acid

medium acid

slightly acid

very slightly acid

neutral

very slightly alkaline

slightly alkaline

medium alkaline

strongly alkaline

cabbage

cauliflower

celery

cucumber

potato

peas

strawberry

tomato

6.0 – 7.5

6.5 – 7.5

6.5 – 7.5

5.5 – 7.0

5.0 – 6.0

6.0 – 7.5

5.0 – 6.0

5.5 – 7.0

pH

10.0

Pho

spho

rus

Nitr

ogen

Pota

ssiu

m

Cal

cium

Mag

nesi

um

Sulfu

r

Iron

Man

gane

se

Bor

on

Cop

per

Zinc

Mol

ybde

num

Minor elementsMinor elements

9.0

8.0

7.0

6.0

5.0

4.0

Easy toabsorb

Difficult toabsorb

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The water cycleCHANGES IN MATTER

The water cycle Earth’s water is always moving in a

cycle called the hydrologic or watercycle.

The Sun provides the energy drivingthe cycle.

1 Evaporation Heat energy causes water to evaporate

from the surface of the oceans, leavingall dissolved substances behind. Therate of evaporation is greater in areasof Earth where the seas are warmer.

Water vapor rises into the atmosphere,where it eventually condenses to formclouds. These are dispersed by winds,which carry them to the colder regionsof Earth.

2 Transportation When clouds reach landmasses, they

are carried up on convection currents.As they rise, the temperaturedecreases, and eventually the watervapor condenses, formingprecipitation, which falls to Earth.

Rainwater contains dissolved gases,which makes it slightly acidic.

3 Deposition The fresh water flows over rocks and

through soils before gathering instreams and rivers. As the water flowsthrough the ground, solids dissolve init.

Water is removed from rivers for bothindustrial and domestic use. Much ofthis water is ultimately returned to therivers. Finally, the water flows out tosea, thus completing the cycle. Anydissolved solids are carried in it andeventually deposited in the oceans.

56

atmosphereconvection

current

Key words

transportation

condensation

surface runoff groundwater flow

precipitation

evaporation1 Evaporation

2 Transportation

3 Deposition

evaporation

evaporation

CHANGES IN MATTER

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Treatment of water andsewage

1 Water treatment Particles are removed from water by

passing it through a series of sandfilter beds and sedimentation tanks.The filter beds also contain bacteria,which break down and destroy micro-organisms in the water.

Chlorine is a powerful oxidizing agentthat is used to kill any remainingmicroorganisms in the water before isstored ready for distribution. Storagetanks are covered to prevent the entryof foreign bodies.

2 Sewage treatment Raw sewage cannot be released into

rivers because of the threat to healthand the effects on the environment.The waste materials it contains mustfirst be broken down by the action ofdecomposing bacteria.

Solids are removed from the sewageby a series of screens and settlingtanks. The remaining liquid passes intoa digester, where bacteria break downthe waste products. Streams of air areblown into the tank in order toprovide the bacteria with the oxygenneeded to survive and to keep themixture circulating.

After settling, the clean water isallowed to pass into the river, whilethe sludge undergoes furtherdigestion during which methane isreleased. The digested sludge containsnitrogenous compounds and is oftenused as a fertilizer.

methaneoxidizing agentsewage

Key words

1 water treatment

2 Sewage treatment

a screenb pumpc sedimentation tankd water ine coarse sand filterf fine sand filterg chlorine addedh covered storage tank

i to homes and factoriesj sewage ink settling tankl digester aeration tankm sludge collectedn clean water to rivero methane outp digested sludge out

a b

cd

j

k

l

m

n

o

p

e f

a b cc

g b

h

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The water moleculeCHANGES IN MATTER

1 A covalent compound Water is essentially a covalent

compound formed by two atoms ofhydrogen and one atom of oxygen.

2 The water molecule The oxygen atom in a water molecule

has two pairs of bonding electrons(sometimes called shared pairs) andtwo pairs of non-bonding electrons(sometimes called lone pairs).

These four pairs of electrons aredirected toward the corners of atetrahedron. However, the tetrahedralshape is distorted. The non-bondingpairs of electrons repel each othermore strongly than the bonding pairsof electrons. Repulsion between theseand the bonding pairs of electronsreduces the angle between theoxygen–hydrogen bonds to 104.5 °.

3 The polar nature of themolecule Oxygen is more electronegative than

hydrogen and, therefore, has astronger attraction for the electrons inthe oxygen–hydrogen bond. The resultis that the electrons in the bond residecloser to the oxygen atom. Sinceelectrons are negatively charged, thisleaves the oxygen atom slightlynegative and the hydrogen atomslightly positive. This is shown using dnotation; oxygen is d- and hydrogen isd+.

58

bondcovalent

compoundhydrogenlone pair

oxygen

Key words

δ+

δ–

δ+

HH

O

O

H

H

H

O

H

O

1 A covalent compound

3 The polar nature of the molecule

2 The water molecule

Atoms present Full shells of a water molecule

shared pairs nearer the oxygen

one outer-shellelectron

six outer-shell electrons

one outer-shellelectron

Bonding pairs

104.5°H

O

HH

O

HWater molecule Non-bonding pairs

(lone pairs)

CHANGES IN MATTER

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Water as a solvent ofionic salts

1 Ionic lattices The ions in an ionic crystal are

arranged in a lattice. Each ion issurrounded by a number of oppositelycharged ions. The lattice structure isdetermined by:- the ratio of the number of positivelycharged ions (cations) to negativelycharged ions (anions)- the ratio of the radii of the ions(rcation / ranion)

The radius ratio in sodium chloride is0.57. The ions are arranged in a face-centered cubic structure in whicheach sodium ion is surrounded by sixchloride ions, and each chloride ion issurrounded by six sodium ions.

The radius ratio of cesium chloride is0.94 (due to the larger cesium ion).The ions are arranged in a body-centered cubic structure in whicheach cesium ion is surrounded byeight chloride ions, and each chlorideion is surrounded by eight cesiumions.

2 The effect of water on anionic lattice When an ionic compound is placed in

water, the water molecules collide withthe lattice. If the water moleculescollide with sufficient energy toovercome the forces of attractionbetween the oppositely charged ions,hydration occurs, and the compoundwill dissolve, forming a solution.

anionbody-centered

cubiccationface-centered

cubic

hydrationionic crystallattice

Key words

The ions attract the water moleculesIonic lattice put into water

The lattice starts to split up

a latticeb water molecules

c charged ends of molecules attractedto ions of opposite charge

2 The effect of water on an ionic lattice

a

b

c

Cl– ion

Na+ ion

H H

O

HH

O

HH

O

HH

OH

H O

H H

O H H

OH

H

O

H

HO

H

HO

O

H

H

H

H O

HH

O

H

H

OH H

O

H

H

O

H

HO

1 Ionic lattices

Cs+ ion

Cl– ion

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Ionic solutionsCHANGES IN MATTER

Ionic solutions Ionic solutions are ionic compounds

dissolved in water.

1 Stabilizing free ions Due to the uneven sharing of

electrons in the oxygen–hydrogenbonds of a water molecule, the oxygenatom is slightly negatively charged andthe hydrogen atoms are slightlypositively charged.

Water molecules surround andstabilize the ions in the compound:positively charged cations arestabilized by the negative oxygenatoms, and negatively charged anionsare stabilized by the positive hydrogenatoms.

2 Transition metals insolution Transition metal ions form complexes

with water. Transition metals have an incomplete

outer shell and can fill this with theelectric charge on the water molecule.Non-bonding pairs of electrons fromthe water molecules are donated toform coordinate bonds.

The bonds between the metal ions andwater are so strong that they remainwhen solids are obtained from theirsolutions.

3 Production of silverchloride When silver nitrate solution and

sodium chloride solution are mixed,insoluble silver chloride forms a whiteprecipitate.Ag+(aq) + Cl-(aq) AgCl(s)

The silver ions and chloride ions aremore stable when bonded together inan ionic lattice than existing apartsurrounded by water molecules.

60

anionbondcationionionic compound

latticetransition metals

Key words

NO–3

NO–3

Silver nitrate solution and sodium chloridesolution

After reaction, clusters of watermolecules have been forced away fromaqueous silver and chloride ions toleave solid silver chloride

1 Stabilizing free ions

Ag+

2 Transition metals in solution

Cl– Cl–

Cl– Cl–

Cl–

Ag+

Ag+Ag+

Ag+

Na+Na+ Cl–

3 Production of silver chloride when a metal chloride isadded to silver nitrate solution

M

O

H H

O

O O

H

H H H

H

H

O O

HH

HH

O

H

HO

H

HH+ H

O

H H

OH

H

O

H H

O-

H H

O

H

HO

H H

O

H H

O

H H

O

H H

O

H

H O

H

HO

H H

O

HH

O

H

H

O

HH

O

HH

O

HH

O

H

HO

H H

O

H

HOO

H

HO

H

H

O

H

H

H H

O

H

HO

H

H

OO

H

HH H

O

H

O H

HH

O

HH

O

H

H O

H

HO

H

OH

H

OHH H

O

H H

O

HH

O

H

H O

HH

O

negatively chargedoxygen atom

positively chargedhydrogen atom

CHANGES IN MATTER

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Solubility

1 Solubility of ioniccompounds All ionic compounds are soluble in

water to some extent. However thesolubility of some is so low that theyare best regarded as insoluble.Solubility generally follows thefollowing rules.

All ammonium, potassium, andsodium salts are soluble.

All nitrates are soluble. With the exception of lead and sliver

bromides, chlorides, and iodides,bromides, chlorides, and iodides aresoluble.

Most sulfates are soluble, with theexception of barium and lead sulfate.

Most carbonates are insoluble, withthe exception of ammonium,potassium, and sodium carbonate.

Most hydroxides are insoluble, withthe exception of ammonium,potassium, and sodium hydroxides.

Calcium hydroxide is only slightlysoluble.

2 Most abundantcompounds in seawater Seawater is a solution of many

different salts. The main salt present inseawater is sodium chloride.

The concentration of solids inseawater depends on the location. Thesaltiest water occurs in the Red Sea,where there is 40 g of dissolved solidsper 1,000 g of water. The NorthAtlantic is the saltiest of the majoroceans, with an average of 37.9 g ofdissolved solids per 1,000 g of water.The least salty waters are found inpolar seas and the Baltic Sea, whichcontains only 5–15 g of dissolvedsolids per 1,000g of water.

ionic compoundinsolublesoluble

Key words

sodiumchloride

78 %

magnesiumchloride

9 %

magnesiumsulfate

7 %

calciumsulfate

4 %

potassiumchloride2 %

calciumcarbonate<1 %

magnesiumbromide

<1 %

1 Table of solubility of ionic compounds

Soluble Insoluble

all salts of ammonium, potassium, andsodium

all nitrates

most bromides, chlorides, and iodides

most sulphates (calcium sulfate isslightly soluble)

ammonium, potassium, and sodiumcarbonate

ammonium, potassium, and sodiumhydroxides (calcium hydroxide is slightlysoluble)

2 Table of the most abundant compounds in seawater

Name of compound Formula of compound Percentage of solidsin seawater

sodium chloride

magnesium chloride

magnesium sulphate

calcium sulphate

potassium chloride

calcium carbonate

magnesium bromide

NaCl

MgCl2

MgSO4

CaSO4

KCl

CaCO3

MgBr2

78

9

7

4

2

less than 1

less than 1

lead and silver bromides, chlorides, andiodides

barium and lead sulfate

most other carbonates

most other hydroxides

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Solubility curvesCHANGES IN MATTER

Expressing solubility Solubility is normally expressed in

g / 100 g of water. The solubility of acompound varies (normally increases)with temperature, so when quotingsolubility, it is necessary to state thetemperature for which it is given.

A solubility curve is a graph thatshows how the solubility of a saltvaries between 0°C (the freezing pointof water) and 100°C (the boiling pointof water).

The solubility curve of a compound isplotted using data about the solubilityof the compound over the wholetemperature range. Solubility curvesare generally not straight lines.

Over the temperature range 0–100°C,the solubility of some salts remainsnearly constant (sodium chloride),while the solubility of others eitherincreases gradually (potassium sulfate)or increases very rapidly (potassiumnitrate).

62

solubility curve

Key words120

110

Mas

sof

crys

tals

that

diss

olve

in10

0g

ofw

ater

(g)

Temperature (°C)

90

100

100

80

70

60

50

40

30

20

10

00 10 20 30 40 50 60 70 80 90

a

b

c

a potassium nitrateb sodium chloridec potassium sulfate

CHANGES IN MATTER

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Solubility of copper(II)sulfate

1 Solubility of copper(II)sulfate at differenttemperatures When no more solid will dissolve in a

solution at a given temperature, thesolution is said to be saturated.

Normally when a solution is cooledbelow the saturation temperature forthe quantity of solute present, somesolute crystallizes out. Under certainconditions a solution may be cooledbelow this temperature withoutcrystallization occurring. Such asolution is said to be supersaturated.

A solubility curve is plotted by findingthe amount of solid needed to make asaturated solution at a number ofdifferent temperatures over the range0–100°C.

2 Solubility curve forcopper(II) sulfate The solubility of copper(II) sulfate at

76°C is found by drawing a vertical linefrom 76°C to the solubility curve andthen a horizontal line to the solubilityaxis. The value is 52 g of copper(II)sulfate per 100 g of water.

The temperature at which thesolubility of copper(II) sulfate isexactly 36 g per 100 g of water isfound by drawing a horizontal linefrom 36 g / 100 g water to thesolubility curve and then a vertical lineto the temperature axis. Thetemperature is 54°C.

The solubility of copper(II) sulfate at90°C is 64.8 g / 100 g water and at 20°Cis 20.7 g / 100 g water. If 100 g ofsaturated copper(II) sulfate solutionwas allowed to cool from 90°C to 20°Cthe mass of copper(II) sulfate crystalsformed would be 64.8 – 20.7 = 44.1 g.

The size of crystals formed is relatedto how quickly the solution is cooled.If cooling is rapid many small crystalsare formed but if cooling is slow asmaller number of large crystals areformed.

saturatedsolutesolutionsolubility curve

Key words

+

+

+

+

+

+

+

+

+

2 Solubility curve for copper(II) sulfate

1 Table of solubility of copper(II) sulfate atdifferent temperatures

Temperature °C Solubilityg/100g water

14.3

17.4

20.7

24.3

28.5

34.0

60

70

80

90

100

40.0

47.1

55.0

64.8

75.4

Temperature °C Solubilityg/100g water

0

10

20

30

40

50

Sol

ubili

tyg/

100

gw

ater

100

70

60

50

40

30

20

10

00 10 20 30 40 50 60 70 80 90

Temperature (°C)

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Hydrogen: preparationPATTERNS—NON-METALS

1 Obtaining hydrogen usingKipps apparatus Traditionally, hydrogen is generated

using a Kipps apparatus. When the tapis opened, dilute hydrochloric acidfloods the bottom compartment andthe level rises until it reacts withgranulated zinc in the middlecompartment. Zinc reacts with dilutehydrochloric acid to producehydrogen:Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

If the tap is closed, hydrogencontinues to be produced for a shorttime, and the pressure of the gas inthe middle compartment graduallyincreases. Eventually the pressure issufficient to force the dilutehydrochloric acid back down and outof the middle compartment, and thereaction stops.

In a modern laboratory, hydrogen isoften obtained directly from a cylinderof the gas.

2 Collecting dry hydrogen A dry gas is a natural gas from which

all water vapor has been reduced. Hydrogen is dried by passing through

anhydrous calcium chloride. The gasis collected by upward delivery(downward displacement of air)because it is less dense than air.

64

2 Collecting dry hydrogen

a

b

c

ac

1 Obtaining hydrogen using Kipps apparatus

a granulated zincb dilute hydrochloric acidc hydrogen gas

a damp hydrogen fromKipps apparatus

b anhydrous calciumchloride

c gas

b

anhydrousdry gashydrochloric acidhydrogen

Key words

PATTERNS—NON-METALS

65

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Hydrogen: comparativedensity

b

c

d

e

a hydrogenb air

c porous vesseld manometer

e carbon dioxide

1 Gaseous diffusion of hydrogen in air

a

b

c

d

1B

a

b

c

d

e

b

c

d

2A 2B

1A

2 Gaseous diffusion of carbon dioxide in air

1 Gaseous diffusion ofhydrogen Gases are able to pass into and out of

a porous vessel. Hydrogen is less dense than air, so it is

contained in an inverted beaker (1A). Hydrogen diffuses into the porous

vessel more quickly than air diffusesout of it.

The gas pressure inside the porousvessel increases and becomes greaterthan atmospheric pressure (1B).Liquid is forced up the right side ofthe manometer (an instrument usedto measure the pressure of a fluid).

2 Gaseous diffusion ofcarbon dioxide Carbon dioxide is more dense than

air, so it is contained in an uprightbeaker (2A).

Carbon dioxide diffuses into theporous vessel more slowly than airdiffuses out of it.

The gas pressure inside the porousvessel decreases and becomes lessthan atmospheric pressure. Liquid isforced up the left side of themanometer (2B).

Comparative density Graham’s law of diffusion states that

the rate at which a gas diffuses (r) isproportional to the square root of 1over its density (d):r =1/d

The density of hydrogen is lower thatair. Therefore, it diffuses more quickly.

The density of carbon dioxide ishigher that air. Therefore it diffusesmore slowly.

carbon dioxidediffusionGraham’s lawhydrogen

Key words

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1 Hydrogen and oxygen Electrolysis of dilute sulfuric acid

produces oxygen at the anode(positive electrode) and hydrogen atthe cathode (negative electrode).

At the anode:4OH-(aq) O2(g) + 2H2O(l) + 4e-

At the cathode: 4H+(aq) + 4e- 2H2(g)

A mixture of hydrogen and oxygenexplodes when ignited:2H2(g) + O2(g) 2H2O(g)

2 Hydrogen and air Hydrogen burns in air to produce

water. The hydrogen gas is dried by passing it

through anhydrous calciumcarbonate so any water producedmust be the result of combustion.

Water vapor condenses on the outersurface of the beaker of cold water andcollects in the water glass.

The liquid turns anhydrous blue cobaltchloride paper pink, showing it iswater.

3 Hydrogen and sulfur Hydrogen reacts with sulfur to

produce hydrogen sulfide:H2(g) + S(l) H2S

Hydrogen sulfide turns damp leadacetate paper black due to theformation of lead sulfide:Pb2+(aq) + H2S(g) PbS(s) + 2H+(aq)

4 hydrogen and chlorine A mixture of hydrogen and chlorine

react in bright light. This is an example of a photochemical

reaction. Light provides the energyneeded for the reaction to start:H2(g) + Cl2(g) 2HCl(g)

66

1 Explosion of hydrogen/oxygen mixture

a polyethylene bottle containing dilute H2SO4b platinum electrodesc polyethelene tubingd bunsen flamee loose supportf hydrogen/oxygen mixtureg hydrogen from Kipps apparatush anhydrous calcium chloridei beaker containg cold waterj hydrogen burning

k water collectedl dry hydrogenm boiling sulfurn filter paper soaked in lead acetateo polyethylene bottle containing mixture of

chlorine and hydrogenp powerful light sourceq rubber bungr white fumes of hydrogen chloride

a

b

c

d

g

h

j

k

l

m

n

o

p

e

f

i

b

Preparation of hydrogen and oxygen from electrolysisof sulfuric acid

Explosion technique

2 Hydrogen and air 3 Reaction of hydrogenwith sulfur

Before light is switched on Light is switched on

4 Photocatalytic explosion of hydrogen with chlorine

q r

anhydrousanodecalcium

carbonatecathodeelectrolysis

hydrogen sulfidelead sulfidephotochemical

reactionsulfuric acid

Key words

Hydrogen: reaction withother gases


67

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Period number

H2O

NH3 H2Se

H2S

PH3

AsH3

H2Te

SbH3

Xe

Kr

Ar

Ne

expected value for water

expected value for ammonia

2 Strong bonding between water molecules

1 Anomalous boiling points of ammonia and water

Boi

ling

poin

t/°C

100

50

0

–50

–100

–150

–200

–250

–300

group 6 hydrides

group 5 hydrides

group 8 hydrides

2 4

2

1

1 3 5 6

2

1

N

HH

H

H

H

N

H

H

N

H

H

δ+

δ–

δ+

δ–

1 Anomalous boiling pointsof ammonia and water Atoms of the group 8 elements have a

full outer orbital of electrons. Theyexist as single atoms, and there arevery weak forces of attraction betweenthem. The boiling point of theseelements increases in proportion tothe size of the atom.

The boiling points of the group 5 andgroup 6 hydrides also increases withmolecular size. However, the boilingpoint of water and ammonia aresignificantly higher than might beexpected when compared to the otherhydrides in their groups. This is theresult of strong forces of attraction,called hydrogen bonding, betweenwater molecules and betweenammonia molecules.

2 Strong bonding betweenwater molecules There are five electrons in the outer

orbital of a nitrogen atom. Inammonia, three of the electrons areused in nitrogen–hydrogen bonds,while the remaining two form a non-bonding or lone pair.

The nitrogen atom in ammonia ismore electronegative than thehydrogen atoms. The result is that apair of bonding electrons lies nearer tothe nitrogen atom than the hydrogenatom in each nitrogen–hydrogenbond.

This forms a dipole, a chemicalcompound with an unequallydistributed electric charge. Thenitrogen–hydrogen bond is polarized,leaving the nitrogen slightly negative(sometimes shown as d-) and thehydrogen slightly positive (sometimesshown as d+).

The slightly positive hydrogen atom isattracted to the slightly negativenitrogen atom and the non-bondingpair of electrons on neighboringammonia molecules.

ammoniaboiling pointdipolegroup 5group 6

group 8hydridelone pairorbital

Key words

Hydrogen: anomalies inammonia and water

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Basic reactions ofhydrogen


1 Preparation Water, in the form of steam, can be

reduced by either carbon orhydrocarbons to give hydrogen.

This reaction is used to providehydrogen for the Haber process in theindustrial manufacture of ammonia(See page 74):CH4(g) + H2O(g) CO(g) + 3H2(g)

2 Reactions of hydrogen Hydrogen forms hydrides with both

metals and non-metals. Hydrogen can be used to reduce the

oxides of metals that are low in thereactivity series, such as copper(II)oxide.

3 The oxides Hydrogen reacts with oxygen to form

both an oxide (water) and a peroxide(hydrogen peroxide).

Hydrogen peroxide contains anunstable peroxide –O-O- bond.

A variety of substances, includingmanganese(IV) oxide, act as catalyststo break this bond, forming water andoxygen.

4 The hydroxy compounds All metal hydroxides are bases. Metal hydroxides that dissolve in water

are alkalis. Sodium hydroxide solution can be

used to form precipitates of insolublemetal hydroxides like copper(II)hydroxide.

5 Acids All acids produce solutions containing

hydrogen ions, H+.

68

1A from coal1B from oil1C electrolysis of brine1D laboratory preparation2A it reduces other elements2B it reduces compound

3A water3B hydrogen peroxide4 metallic hydroxides are bases

5 Acids

HCl H+ + Cl–

HNO3 H+ + NO3–

H2SO4 2H+ + SO42–

2 Reactions of hydrogen

CuO + H2 Cu + H2O

2Na + H2 2NaH

N2 + 3H2 2NH3

O2 + 2H2 2H2O

Cl2 + H2 2HCl

1 PreparationC + H2O CO + H2

C7H16 + 7H2O 7CO + 15H2

2H2O + 2e– 2OH– + H2

Zn + 2HCl ZnCl2 + H2

4 The hydroxy compounds

NaOH + HCl NaCl + H2O

2NaOH + CuCl2 Cu(OH)2↓ + 2NaCl

3 The oxides

2Na + 2H2O 2NaOH + H2

2H2O2 2H2O + O2MnO2

A

B

C

D

A

B

B

A

alkalibasecatalysthydridehydrogen

hydrocarbonhydroxideoxideperoxide

Key words


69

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The gases in air

Nitrogen Carbon dioxide Argon Oxygen

3 Gases that may be found in polluted air

Gases Symbol or formula

NH3

CO

CH4

NOx

O3

SO2

Industrial processes

Motor vehicle exhaust

Decay of organic material, passed in windby herbivorous animals

Motor vehicle and furnace exhaust

Motor vehicle exhaust

Ammonia

Carbon monoxide

Methane

Nitrogen oxides

Ozone

Sulphur dioxide

Example of source

Coal-fired power stations

2 Gases present in clean dry air

Gases Symbol or formula

Nitrogen

Oxygen

Neon

Helium

Krpton

Xenon

Percentage of volume

Argon

Carbon dioxide

N

O

Ne

He

Kr

Xe

Ar

CO2

78.08

20.95

traces

0.93

0.04

1 Composition of air

1 Composition of air Air is not a chemical compound but a

mixture of elements and compounds.The exact composition of air variesslightly from place to place dependingon conditions. For example, theproportion of carbon dioxide in theair above a forest will be less than inthe air above a city. Trees removecarbon dioxide for photosynthesis,while burning fossil fuels releasescarbon dioxide.

2 Gases present in cleandry air Clean dry air is approximately 80

percent nitrogen and 20 percentoxygen.

Argon makes up the largest portion ofthe remaining 10 percent.

Air usually contains water vapor, withthe amount depending on localconditions.

3 Gases in polluted air Air may contain pollutants released

from a variety of sources. Sulfur dioxide and nitrogen oxides

dissolve in water in the atmosphereand increase the acidity of rainwater.

Carbon monoxide is a poisonous gas.If it is inhaled, it bonds onto thehemoglobin in red blood cells andprevents them from transportingoxygen.

Ozone is essential in the upperatmosphere (ozone layer), where itprevents harmful ultraviolet radiationfrom reaching Earth. At ground level,however, it is responsible for theformation of smog.

Methane and carbon dioxide aregreenhouse gases. In the upperatmosphere, they prevent heatradiation from passing out into space,thus causing the global temperature torise.

argoncarbon dioxidecarbon monoxidecompoundelement

methaneozonepollutantsulfur dioxide

Key words

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NitrogenPATTERNS—NON-METALS

1 Nitrogen atom andmolecule Nitrogen is in group 5 of the periodic

table. Nitrogen atoms have fiveelectrons in the outer orbital andrequire an additional three electronsin order to fill the shell.

Nitrogen exists as nitrogen molecules,N2, in which each nitrogen atomprovides three electrons. The nitrogenatoms are held together by a triplebond. A large amount of energy isneeded to break the N[N triple bond(945.4 kJ mol-1), which accounts forthe unreactive nature of nitrogen.

2 Physical properties ofnitrogen The melting point and boiling point of

nitrogen are both very low, andnitrogen is only a liquid over a smallrange of temperature. This indicatesthat the intermolecular forces innitrogen are weak.

The solubility of gases decreases withincreasing temperature. The solubilityof nitrogen falls from 2.3 cm3 per 100 gwater at 0°C to 1.0 cm3 per 100 g waterat 100°C.

3 Laboratory preparationof nitrogen Nitrogen is formed by the thermal

decomposition of ammonium nitrite:NH4NO2(s) 2H2O(g) + N2(g)

Ammonium nitrite is difficult to storebecause it decomposes over time. It isbest made when it is needed by mixingammonium chloride and sodiumnitrite:NH4Cl(s) + NaNO2(s)

NH4NO2(s) + NaCl(s)

70

3 Laboratory preparation of nitrogen from ammoniumchloride and sodium nitrate

a ammonium chloride and sodiumnitrate in solution

b heatc sand trayd nitrogene water

a

b

c

d

e

1 Nitrogen atom and molecule

N N N

Nitrogen atom, 147N Nitrogen molecule, N2

Physicalproperties

Nitrogen –120 –196 0.97 none none1.52 cm3

in 100gof water

m.p./°Cdensity(relativeto air)

color smell

2 Physical properties of nitrogen

solubilityat STPb.p./°C

group 5nitrogensolubilitytriple bond

Key words


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Other methods ofpreparing nitrogen

2 Preparation of nitrogen from ammonia

1 Extraction of nitrogen from the atmosphere

d

j

g

h

e

fi

d

a

b

c

d

g

h

e

f

d

a air intakeb potassium hydroxide solution to absorb carbonc hot copper coil to remove oxygend heate safety trapf delivery tube

g waterh nitrogen collected over wateri dry ammonia gasj dry copper(II) oxide

Other methods In addition to preparing nitrogen from

ammonium chloride and sodiumnitrate, it can be extracted from the airor from the reduction of copper(II)oxide by ammonia.

1 Extraction of nitrogenfrom the atmosphere Air is approximately 80 percent

nitrogen and 20 percent oxygen.Impure nitrogen can be obtained byremoving carbon dioxide and oxygenfrom air.

Potassium hydroxide solution reactswith carbon dioxide:KOH(aq) + CO2(g) KHCO3(aq)

A hot copper pile reacts with oxygen:2Cu(s) + O2(g) 2CuO(s)

Nitrogen prepared in this way containsargon and other group 8 gases.However, because these are chemicallyinert, they would not interfere withany subsequent reactions.

2 Preparation of nitrogenfrom ammonia Ammonia can be used to reduce

copper(II) oxide to copper. Nitrogen isone of the other products of thisreaction:3CuO(s) + 2NH3(g)

3Cu(s) + 3H2O(g) + N2(g)

Nitrogen is not very soluble and isreadily collected over water.

Water vapor condenses in the watertrough. Ammonia is very soluble, andunreacted ammonia dissolves in thewater.

ammoniagroup 8inertnitrogensoluble

Key words

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The nitrogen cyclePATTERNS—NON-METALS

Nitrogen cycle Nitrogen is continually being recycled

between the soil and the air by naturalprocesses.

Lightning provides the energy foratmospheric nitrogen and oxygen toreact, forming nitrogen oxides. Forexample: N2(g) + O2(g) 2NO(g)

N2(g) + 2O2(g) 2NO2(g)

These oxides dissolve in water vaporin the atmosphere and eventually fallto the ground as rain.

Atmospheric nitrogen is alsoconverted into nitrogen compoundsby nitrogen-fixing bacteria found in theroot nodules of some plants.

Nitrogen compounds are released intothe soil as a result of the decay ofanimal waste products and by thedecay of dead plants and animals. Inthe soil, the ammonia formed duringdecay processes is converted intonitrates by the action of nitrifyingbacteria:Ammonia Ammonium compounds

Nitrites Nitrates Nitrogen compounds may also be

added to soil as artificial fertilizers.Ammonium nitrate is widely used byfarmers and gardeners to providegrowing plants with essential nitrogen.

Nitrogen compounds are taken out ofthe soil by plants, which use them tomake proteins and other essentialchemicals. Animals subsequently eatthe plants.

Nitrogen compounds in the soil areconverted to nitrogen gas bydenitrifying bacteria.

72

1

43

2

5

7

8

6

1 Nitrogen in the air.2 Nitrogen in the atmosphere is trapped by

some plant roots.3 Plants use nitrogen for making proteins.4 Animals eat plant proteins.5 The proteins in dead organisms and in body

wastes are converted to ammonia by bacteria and fungi.

6 Other bacteria convert the ammonia to nitrates.

7 Artificial nitrates are added to the soil as fertilizer.

8 Plants absorb the nitrates.

Nitrogen cycle schematic

All plants and animals need nitrogen, present in proteins and nucleic acids. Most living things,however, cannot use nitrogen directly from the atmosphere.

1

3

2

4

5

6

7 8

Nitrogen cycle

ammonianitratenitritenitrogennitrogen cycle

Key words


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Preparation andproperties of ammonia

107°

3 Physical properties of ammonia

Physical property

Ammonia

Carbon monoxide

Methane

Nitrogen oxides

Ozone

Sulphur dioxide

2 Bonding angle

1 Laboratory preparation of ammonia

–77.7

–33.5

0.59

colorless

characteristic unpleasant odour

68 000 cm3 in 100 g of water

Ammonia

a sodium hydroxideb ammonium chloridec heatd calcium oxide for dryinge downward displacement of air

NH

H

HNH

H

H

a

b

c

d

e

1 Laboratory preparation ofammonia Ammonia is formed by the reaction of

an ammonium compound, such asammonium chloride, with an alkali,such as sodium hydroxide:NH4Cl(s) + NaOH(aq)

NH3(g) + NaCl(aq) + H2O(l)

Ammonia gas is dried by passing itthrough a column of calcium oxide.

2 Bonding angle The five electrons in the outer

electron shell of nitrogen plus threeshared electrons from the hydrogenatoms form three pairs of bondingelectrons and one pair of non-bondingelectrons (lone pair).

The four pairs of electrons aredirected toward the corners of atetrahedron. However, repulsionbetween the non-bonding pair ofelectrons and the bonding pairs ofelectrons forces thenitrogen–hydrogen bonds slightlycloser to each other, resulting in abond angle of 107°. By comparison,the bond angle in methane is 109.5°.

3 Physical properties ofammonia Ammonia is less dense than air and is

collected by upward delivery(downward displacement of air).

Ammonia is exceptionally soluble andcannot be collected over water.680 cm3 of ammonia will dissolve in1 g of water at 20°C.

Ammonia dissolves in water to form asolution that is a weak alkali:NH3(g) + H2O(l)

NH4+(aq ) + OH-(aq)

Ammonia solution is sometimesreferred to as ammonium hydroxide.

alkaliammoniaammonium

hydroxidebond angle

lone pairshell

Key words

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Industrial preparation ofammonia (the Haberprocess): theory


1 Reversible reaction Ammonia is made industrially by the

reaction of nitrogen and hydrogen. The reaction is reversible.

Forward reaction:N2(g) + 3H2(g) 2NH3(g)

Backward reaction:N2(g) + 3H2(g) 2NH3(g)

The concentration of ammonia in theequilibrium mixture depends on thepressure and temperature at which thereaction is carried out.

According to Le Chatelier’s principle,if any change is made to the externalconditions (such as temperature,concentration and pressure) of asystem at equilibrium, the equilibriumposition will alter so as to oppose thechange.

2 Variation of percentammonia with pressure In the forward reaction, four moles of

reactants are converted into twomoles of product so there is a drop inpressure.

According to Le Chatelier’s principle,an increase in pressure will favor theforward reaction. The equilibriumposition will move to the right in orderto oppose the increase in pressure, sothe equilibrium mixture will containmore ammonia.

3 Variation of percentammonia with temperature The reaction is exothermic; heat is

given out. According to Le Chatelier’s principle, a

decrease in temperature will favor theforward reaction. The equilibriumposition will move to the right in orderto oppose the decrease intemperature, so the equilibriummixture will contain more ammonia.

74

ammoniaequilibriumLe Chatelier’s

principle

productreactant

Key words

Pressure (atm)

Temperature (°C)

Equ

ilibr

ium

%of

amm

onia

100

90

80

70

60

50

40

30

20

10

0100 30025 200 400

1 Reversible reaction

N2(g) + 3H2(g) 2NH3(g) ∆H = –92 kJ mol–1

4 moles 2 moles

2 Variation of percent ammonia with pressure

3 Variation of percent ammonia with temperature

500°C

400°C

300°C

200°C100°C

Equ

ilibr

ium

%of

amm

onia

100

90

80

70

60

50

40

30

20

10

0100 3000 200 400

400 atm200 atm100 atm50 atm25 atm

Variation of % ammoniawith temperature

Working rangeof catalyst


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Industrial preparation ofammonia (the Haberprocess): schematic

Hydrocarbons Liquid air

Steamreforming

Fractionaldistillation

Hydrogen Nitrogen

ReactorTemperature:

370–450°CPressure:

80–110 atmCatalyst:

iron

Liquidammonia

Unreactedhydrogen and

nitrogen

Coolingbelow –33.5°C

The process The raw materials for the Haber

process are hydrogen and nitrogen. Hydrogen is obtained by the steam

reforming of hydrocarbons, such asmethane, or the reaction of steam withcoke.CH4(g) + H2O(g) CO(g) + 3H2(g)

C(s) + H2O(g) CO(g) + H2(g)

Nitrogen is obtained from thefractional distillation of liquid air.

The formation of ammonia is favoredby high pressure, and the reaction isnormally carried out at 80–110 atm. Itis also favored by low temperature, butthis also lowers the rate of reaction, soa catalyst is used. The reaction isnormally carried out at 370–450°C inthe presence of a finely divided ironcatalyst.

In reality, the reaction is not allowed toreach equilibrium. A single passthrough the reactor results in about 15percent conversion to ammonia.

The reaction mixture is cooled tobelow the boiling point of ammonia, atwhich point liquid ammoniacondenses out and is removed. Themixture of unreacted hydrogen andnitrogen is recycled back into thereactor.

Around 80 percent of the ammoniaproduced each year is used to makefertilizers, including ammonia solution,ammonium nitrate, ammonium sulfate,and urea.

ammoniacatalystequilibriumfractional

distillation

hydrocarbonhydrogennitrogen

Key words

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Industrial preparation of nitric acid


1 Preparation The industrial production of nitric

acid involves two stages: theoxidation of ammonia and theabsorption of the resulting nitrogenoxides.

In the converter, a mixture ofammonia and air is passed through aplatinum–rhodium gauze and theammonia is oxidized:4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

DH = -909 kj mol-1

The reaction is exothermic, and a largequantity of heat is produced.

Conditions are carefully controlled tominimize a competing reaction inwhich ammonia is oxidized tonitrogen:4NH3(g) + 3O2(g) 2N2(g) + 6H2O(g)

Air is added to the nitrogen oxides inorder to make nitrogen dioxide and,subsequently, dinitrogen tetroxide.2NO(g) + O2(g) 2NO2(g)

2NO2(g) N2O4(g)

Dinitrogen tetroxide reacts with waterto produce nitric acid.3N2O4(g) + 2H2O(l)

4HNO3(aq) + 2NO(g)

The acid from the absorption towerstypically contains 55–60 percent nitricacid by mass. Most of the moderndemand is for acid of thisconcentration.

Nitric acid and water form anazeotropic mixture (a mixture thatboils without a change incomposition) containing 68.5 percentnitric acid by mass. Thus, concentratednitric cannot be obtained bydistillation. Concentrated sulfuric acidis used to reduce the water contentand give concentrated nitric acid.

2 Uses of nitric acid Over two thirds of nitric acid

production is directed to makingammonium nitrate, which is used as afertilizer and in explosives.

76

ammoniaazeotropic

mixtureexothermicnitric acid

oxidation

Key words

a

b

c

d

g h j

k

e

f

i

1 Industrial manufacture of nitric acid

2 Summary of uses

79%Ammonium nitrate

12%Nitro

aromatics 9%Adipicacid

a airb ammoniac powerd platinum rhodium catalyste oxidation reactionf NO, NO2, O2g waterh reaction with wateri pumpj nitric acidk unreacted gas


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Nitrogen: reactions inammonia and nitric acid

A

X

XX

X

1 Redox chemistry (ammonia)

2NH3 + 3Cl2 N2 + 6HCl

2 Redox chemistry (nitric acid)

2NH3 + 3CuO 3Cu + 3H2O + N2

Ammonia reduces chlorine to hydrogen chloride and nitrogen

Ammonia reduces copper oxide to copper, water, and nitrogen

C + 4HNO3 CO2 + 4NO2 + 2H2O

3Cu + 8HNO3(dilute) 3Cu(NO3)2 + 4H2O + 2NO

Concentrated nitric acid oxidizes carbon to carbon dioxide

Dilute nitric acid oxidizes copper to produce copper nitrate, water, and nitrogen oxide

Concentrayed nitric acid oxidizes copper to produce copper nitrate,water, and nitrogen dioxide

→

Cu + 4HNO3(conc) Cu(NO3)2 + 2H2O + 2NO2 →

4 Tetraamminecopper(II) ion

3 Complex ammonia salts

Ammonia solutionis addedto CuSo4 solution

More ammonia solutionis added

The precipitate diasppears,leaving a deep royal bluesolution (a complex salt)

ammoniasolution

pale blueprecipitate

Square planar

1 Redox chemistry(ammonia) Ammonia is a reducing agent and will

reduce chlorine and heated metaloxides such as copper oxide. Duringthe reactions, the ammonia is oxidizedto nitrogen.

2 Redox chemistry (nitric acid) In addition to its properties as an acid,

nitric acid is also a powerful oxidizingagent. It is able to oxidize both non-metals and metals.

3 Complex ammonia salts When ammonia solution is added drop

by drop to copper(II) sulfate solution,a pale blue precipitate of copper(II)hydroxide is formed:Cu2+(aq) + 2OH-(aq) Cu(OH)2(s)

When an excess of ammonia solutionis added, the pale blue precipitateredissolves, forming a deep bluesolution:Cu(OH)2(s) + 4NH3(aq)

[Cu(NH3)4]2+

The deep blue solution contains thecomplex ion tetraamminecopper(II),[Cu(NH3)4]2+.

Ammonia also forms complex ionswith other metals, such asdiamminesilver(I), [Ag(NH3)2]+ andhexaamminenickel(II), [Ni(NH3)6]2+.

4 Tetraamminecopper(II) In the tetraamminecopper(II) ion, a

copper ion is surrounded by fourammonia molecules in a square planararrangement. The non-bonding pair ofelectrons on each nitrogen atom isattracted to the central positivelycharged copper ion.

ammonianitric acidoxideoxidizing agentreducing agent

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Basic reactions ofnitrogen


1 With metals and non-metals Nitrogen combines directly with both

metals, such as magnesium, and non-metals, such as sodium and hydrogen.

2 Basic reactions ofammonia Ammonia reacts with water to

produce a soluble alkaline gas (2A). Ammonia reacts with an acid to

produce a salt (2B). Ammonia reacts with an oxide to

produce a metal and nitrogen (2C). Ammonia reacts with oxygen to

produce nitric acid (2D).

3 Nitric acid Nitric acid is both a strong acid (3A)

and a powerful oxidizing agent (3B). Cold, dilute nitric acid produces

nitrogen oxide when reacting with ametal (3C).

Hot, concentrated nitric acid producesnitrogen dioxide when reacting with ametal (3D).

4 Nitrates All nitrates are very soluble in water. Group 1 metal nitrates (apart form

lithium nitrate) decompose on heatingto form metal nitrites and oxygen.

Other metal nitrates decompose onheating to form metal oxides, nitrogendioxide, and oxygen.

Ammonium nitrate decomposes onheating, forming water and dinitrogenoxide.

78

acidammonianitratenitric acidnitrite

nitrogenoxideoxidizing agentsalt

Key words

2A soluble alkaline gas2B reducing agent2C ammonia with oxygen to make nitric acid2D complexing agent3A strong acid3B oxidizing agent

4A group 1 (excluding LiNO3)4B others4C ammonium nitrate

1 With metals and non-metals

3Mg + N2 Mg3N2

6Na + N2 2Na3N

N2 + 3H2 2NH3Fe catalyst

2 Basic reactions of ammonia

2NH3 + 3CuO 3Cu + 3H2O + N2

2NO + O2 2NO2

A

4NH3 + 5O2 4NO + 6H2O

4NO2 + O2 + 2H2O 4HNO3

B

then

and

NH3 + H2O NH4+ + OH2

-

C

Cu(OH)2 + 4NH3 Cu(NH3)42+ + 2OH-D

NH3 + HCl NH4Cl

3 Nitric acid

HNO3 + H2O H3O+ + NO3–

C + 2HNO3 CO2 + 2NO2 + H2O

Cu + 4HNO3 Cu(NO3)2 + 2H2O + 2NO2

A

B

2NaNO3 2NaNO2 + O2

2Pb(NO3)2 2PbO + 4NO2 + O2

NH4NO3 2H2O + N2O

A

4 Nitrates

B

C


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Nitrate fertilizers

4 Table of nitrogen fertilizers

Compound

Ammonium nitrate

Ammonium sulphate

Urea

Percentage of nitrogenFormula

NH4NO3

(NH4)2SO4

H2NCONH2

35.00

21.21

46.67

1 Atmospheric nitrogen

NH3(aq) + HNO3(aq) → NH4NO3(aq)

2 Ammonia nitrate

Nitrogen → Ammonia → Nitric acid

Ammonium nitrate

Formula mass of ammonium nitrate = 14 + 4 + 14 + 3 × 16 = 80

Percentage of nitrogen in ammonium nitrate = 2 × 14 × 100 = 35% 80

3 Nitrogen in plants

R

CHH2N COOH

animo acids

proteins

Chlorophyll a(In chlorophyll b, the methyl groupmarked by an asterisk is replaced

by a —CHO group)

CH3 CH CH3

C C

C C CHHC

C CHCH3C

C N

CCH

H NN Mg

NCC

*CH3

CH2CH3

C C C CH

HC C C

CH2

CH2

CHO COC

O

CH3

CH CH

C20H39 CH3

1 Atmospheric nitrogen Atmospheric nitrogen is an important

raw material in the manufacture ofammonia and nitric acid.

Ammonia solution is alkali, whilenitric acid is acidic.

The two solutions undergo aneutralization reaction to form thesalt ammonium nitrate.

2 Ammonia nitrate The percentage of nitrogen in a

nitrogenous fertilizer is an importantfactor in determining how muchfertilizer should be used on an area ofcrops.

Ammonium nitrate is very soluble inwater. Any excess that is applied to soilis readily washed out into streams andrivers, where it causes environmentalproblems.

3 Nitrogen in plants Plants use nitrogen to make amino

acids and, from these, to makeproteins.

Plants also use nitrogen to make otherimportant chemicals, such aschlorophyll.

4 Nitrogen fertilizers Ammonium sulfate is formed by the

neutralization reaction betweenammonia solution and sulfuric acid:2NH3(aq) + H2SO4(aq)

(NH4)2SO4(aq)

Urea is a waste product of animalmetabolism and is excreted from thebody in sweat and urine. It is madeindustrially by the reaction ofammonia with carbon dioxide. Thisreaction is carried out at 200 °C and200 atmospheres:CO2(g) + 2NH3(g)

H2NCONH2(l) + H2O(g)

alkaliamino acidammoniachlorophyllneutralization

nitric acidprotein

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Oxygen and sulfurPATTERNS—NON-METALS

1 Atoms and molecules Oxygen and sulfur are both in group 6

of the periodic table. Atoms of eachelement have six electrons in the outerelectron shell and require twoelectrons to fill the shell.

Oxygen exists as oxygen molecules,O2, in which each oxygen atomprovides two electrons. The oxygenatoms are held together by a doublebond, O=O.

At room temperature, sulfur exists as amolecule composed of eight sulfuratoms, S8, arranged in the shape of acrown.

2 Laboratory preparationof oxygen Oxygen is prepared in the laboratory

by the decomposition of hydrogenperoxide using a suitable catalyst,such as manganese dioxide:2H2O2(l) O2(g) + 2H2O(l)

Hydrogen peroxide is rapidlydecomposed by a variety of catalysts,including the enzyme catalase. In onesecond, one molecule of catalase candecompose up to 50,000 molecules ofhydrogen peroxide.

Oxygen is only slightly soluble and canbe collected over water.

Hydrogen peroxide is usually suppliedin solutions designated by volumestrength. For example, 20-volumehydrogen peroxide yields 20 volumesof oxygen gas per volume of solution.

3 Physical properties ofoxygen and sulfur At room temperature, oxygen is a

colorless, odorless gas, while sulfur is ayellow solid.

80

OO O

S

SS S

S SS

S S

3 Physical properties of oxygen and sulfur

Physical properties

m.p./°C

b.p./°C

Density g/dm3

Color

Smell

Solubility

1 Atoms and molecules

–218

–183

1.31

none

none

0.007g per 100g/H2O

Sulfur

a liquid reactant – hydrogenb solid catalyst – manganese oxidec waterd oxygen

a

c

Oxygen

119

444

2070

yellow

slight

almost insoluble

Sulfur molecule S8(crown-shaped)

Oxygen atom 168O

Sulfur atom 3216S

Oxygen molecule O2

2 Laboratory preparation of oxygen

d

b

catalystdouble bondenzymegroup 6oxygen

sulfur

Key words


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Extraction of sulfur— the Frasch processThe Frasch process

a

b

c

d

g

h

e

f

150m

a hot compressed airb superheated water (at 170°C)c molten sulfur and waterd clay

e quicksandf sandg limestoneh sulfur

Processing and uses Hot compressed air and superheated

steam are piped underground. Thisforces water and molten sulfur to thesurface.

The sulfur obtained is about99.5 percent pure, and may be storedand transported molten or allowed tocool and solidify.

A significant proportion of theelemental sulfur used in industry isobtained as a by-product of otherindustrial processes such as therefining of metal sulfide ores andpetroleum refining.

In petroleum refining, sulfurcompounds like thiols (R-SH) anddisulphides (R-S-S-R) are removedfrom some of the petroleum fractionsbecause they would damage thecatalysts used in refining processesand also because of their potential tocause environmental problems. Forexample, if they were not removedfrom fuels like gasoline, they wouldburn to form sulfur dioxide. This gasdissolves in water in the atmosphere,forming an acid, and wouldsignificantly increase the acidity of rainwater.

Sulfur compounds are converted tohydrogen sulfide by catalytichydrogenation:R-SH(g) + H2(g)

R-H(g) + H2S(g)

R-S-S-R(g) + 3H2(g)

2R-H(g) + 2H2S(g)

Hydrogen sulfide can be converted tosulfur using the Claus process:6H2S(g) + 5O2(g)

2SO2(g) + 2S2(g) + 6H2O(g)

4H2S(g) + 2SO2(g)

3S2(g) + 4H2O(g)

oresulfidesulfursulfur dioxide

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Oxygen and sulfur:allotropes


Allotropes Allotropes are different forms of the

same element in the same physicalstate. Many elements, includingoxygen and sulfur, exist as more thanone allotrope.

1 Oxygen The most common form of oxygen is a

diatomic molecule, O2. The gas alsoexists as a triatomic molecule, O3,which is called ozone.

Oxygen has two bonds between theatoms. Each atom donates oneelectron to each bond.

In ozone, the central oxygen atomdonates a pair of electrons to form abond with the other two atoms. Oneof the other atoms also donates a pairof electrons, while the other does not.

2 Sulfur Sulfur has several allotropes in the

solid form, including rhombic sulfurand monocline sulfur.

Rhombic sulfur crystals have a lemon-yellow appearance.

Monocline sulfur crystals are needle-like and have a deeper yellow color.

Each allotrope is composed of S8puckered molecular rings, butarranged in different ways.

3 Heating sulfur Sulfur melts when gently heated, and

the sulfur molecules are able to movearound, forming a low-viscosity liquid.

On stronger heating, the sulfur ringsbreak open, yielding sulfur molecules.These molecules join by cross-linking,causing a sharp increase in viscosity.

On even stronger heating, the cross-linked structure breaks, yielding smallsulfur molecules, which are free-moving, and the viscosity falls.

82

allotropebonddiatomic

moleculeoxygen

ozonesulfurviscosity

Key words

Rhombicsulfur

Monoclinicsulfur

O

O

O

OO

O O

OO

O– OO

O–

3

Structure

Color

State of matter

Viscosity

1 Allotrope of oxygen

yellow

solid

–

Oxygen Ozone

+ +

yellow

liquid

low

red

liquid

high

black

liquid

low

2 Allotropes of sulfur


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Oxygen and sulfur:compound formation

Oxygen reacts withmagnesiun

Magnesium oxideis ionic

Sulfur and ironglow

Iron sulfide isalso ionic

A tube full of air Phosphorus is added Unreacted phosphorusis left behind

Water is formed whenoxygen and hydrogenare exploded together

Hydrogen peroxide is madeby reacting a metalperoxide with acid

Hydrogen sulfide is madeby the reaction of a metal

sulfide with dilute acid

H

O

H H

S

H

O

H

O

H

O

H

O O

H

H

S

HH H

1 Oxygen and magnesium

a

b

2 Reaction of sulfur and iron

3 Phosphorous reacts with atmospheric oxygen

O2–

Mg2+

S2–

Fe2+

4 Water, hydrogen peroxide, and hydrogen sulfide

a oxgenb magnesium burningc volume scale

d 100 cm3 of aire waterf stiff wire

g phosphorus reactingh 79 cm3 of air is left behind

c

dg

h

e

f

1 Oxygen and magnesium Oxygen reacts with most metals to

form metal oxides. Magnesium burnsin air with a bright flame, producing awhite smoke of magnesium oxide. Thereaction is even more vigorous in pureoxygen:2Mg(s) + O2(g) 2MgO

Soluble metal oxides dissolve in waterto form alkaline solutions:MgO(s) + H2O(l) Mg(OH)2(aq)

2 Sulfur and iron Sulfur forms sulfides with many

metals. When iron and sulfur areheated together, iron sulfide isformed:8Fe + S8 = 8FeS

3 Oxygen and phosphorous Oxygen also reacts with non-metals to

form oxides. Phosphorus burns in airto form phosphorus(V) oxide.Approximately 20 percent of the air isused:P4(s) + 5O2(g) P4O10(s)

Non-metal oxides dissolve in water toform acids:P4O10(s) + H2O(l) 4H3PO4(aq)

4 Other common reactions Hydrogen burns in oxygen to form

water:2H2(g) + O2(g) 2H2O(l)

Hydrogen peroxide is formed by thereaction of metal peroxides, such asbarium peroxide, with dilute acids:BaO2(s) + H2SO4(aq)

H2O2(aq) + BaSO4(s)

Hydrogen sulfide is formed by thereaction of a metal sulfide with a diluteacid:FeS(s) + 2HCl(aq)

FeCl2(aq) + H2S(g)

hydrogenhydrogen

peroxidehydrogen sulfidemagnesium

oxideoxygenperoxidesulfidesulfur

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The oxides of sulfurPATTERNS—NON-METALS

Sulfur oxides Sulfur combines with oxygen to form

two oxides: sulfur dioxide (sulfur(IV)oxide) and sulfur trioxide (sulfur(VI)oxide.

1 Laboratory preparation ofsulfur dioxide Metal sulfites, such as sodium sulfite,

react with dilute acids to from sulfurdioxide:Na2SO3(s) + 2HCl(aq)

2NaCl(aq) + H2O(l) + SO2(g)

Sulfur dioxide is dried by passing itthrough anhydrous calcium chlorideand collected by downward delivery.

Sulfur dioxide dissolves in water toform sulfurous acid:H2O(l) + SO2(g) H2SO3(aq)

2 Laboratory preparationof sulfur trioxide Sulfur trioxide is formed when dry

sulfur dioxide and oxygen are heatedin the presence of a platinizedasbestos catalyst:2SO2(g) + O2(g) 2SO3(g)

Sulfur trioxide forms needle-likecrystals when cooled.

Sulfur trioxide dissolves in water toform sulfuric acid:H2O(l) + SO3(g) H2SO4(aq)

3 SO2 and SO3 molecules In sulfur dioxide, there are four pairs

of bonding electrons and a non-bonding or lone pair of electronsaround the sulfur atom. The pairs ofelectrons are kept as far from eachother as possible by adopting a bentshape in which the double bondsbetween the sulfur and oxygen atomsare at an angle of 120°.

In sulfur trioxide, the three doublebonds form a trigonal planar structurearound the sulfur atom in which thebond angle is also 120°.

84

catalystlone pairoxidesulfitesulfur

sulfur dioxidesulfurous acidsulfur trioxide

Key words

S

O

O

S

O O O

O

S

O O

S

O

O

1 Laboratory preparation of sulfur dioxide

a diluteb sodium sulfitec anhydrous CaCl2d upward displacemente oxygen

f sulfur dioxideg concentrated sulfuric acid

for dryingh plantinized asbestos

i freezing mixture of ice andsalt

j needles of sulfur oxidek to the fume cupboardl 3-way tap

g j

ke

f

i

2 Laboratory preparation of sulfur trioxide

d

a

bc

120°

Molecule of sulfur dioxide Molecule of sulfur trioxide

120°

h

3 SO2 and SO3 molecules

l


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Industrial preparation ofsulfuric acid (the contactprocess): theory1 Sulfur burning

S(1) + O2(g) → SO2(g) ∆H = –297 kJ mol–1

2 Conversion

2SO2(g) + O2(g) 2SO3(g) ∆H = –192 kJ mol–1

4 moles 2 moles

3 Absorption

H2SO4(1) + SO3(g) H2S2O7(1)

H2S2O7(1) + H2O(1) → 2H2SO4(1)

Reaction bed 1

420°C

600°C

450°C

510°C

450°C

475°C

420°C

435°C

63% conversion

84% conversion

93% conversion

99.5% conversion

Reaction bed 2

Reaction bed 3

Reaction bed 4

SO2 O2

SO3(g)to final absorber

remainingSO3

SO3

98% H2SO4

99.5% H2SO4

Heatexchangers

Intermediateabsorber

Preparation of sulfuric acid The industrial preparation of sulfuric

acid is a three stage process:1. Sulfur burning2. Conversion of sulfur dioxide tosulfur trioxide3. Absorption of sulfur trioxide to formsulfuric acid.

1 Sulfur burning Molten sulfur is sprayed into a furnace

and burned in a blast of dry air. Thereaction is very exothermic, and thereaction temperature rises to over1,000°C. The mixture of gases,containing sulfur dioxide and oxygen,is cooled before conversion.

2 Conversion The conversion of sulfur dioxide into

sulfur trioxide is an exothermicreaction. The forward reaction isfavored by a low temperature.However, this would also reduce therate of reaction, so it would takelonger for the reaction mixture toreach equilibrium.

The reaction is carried out attemperatures between 420–620°C inthe presence of a vanadium(V) oxidecatalyst.

Modern converters consist of fourreaction beds. The reaction mixture iscooled after passing through each ofthe first two beds in order to maximizeconversion in subsequent beds.

3 Absorption Sulfur trioxide is removed and

absorbed after the reaction mixturehas passed through both the third andfourth beds.

Sulfur trioxide is absorbed into98 percent sulfuric acid to form99.5 percent sulfuric acid, which issometimes referred to as oleum andgiven the chemical formula H2S2O7.

Oleum is then diluted to give 98percent sulfuric acid.

catalystexothermicequilibriumsulfursulfur dioxide

sulfuric acidsulfur trioxide

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Industrial preparation ofsulfuric acid (the contactprocess): schematic


Preparing sulfuric acid The sulfur needed for the

manufacture of sulfuric acid isobtained either directly from theground or as a by-product of otherindustrial processes, such as therefining of metal sulfide ores and therefining of crude oil.

An excess of dry air is used to ensurethere is sufficient oxygen remaining inthe reaction mixture for theconversion of sulfur dioxide to sulfurtrioxide.

The vanadium(V) oxide (vanadiumpentoxide) catalyst is activated bypotassium sulfate on a silica support. Itis generally in the form of smallcylindrical pellets that ensure a largesurface area for reaction. The catalystis inactive below about 380°C and hasan optimum working temperaturebetween 420–620°C.

The catalyst pellets are packed ontoperforated plate supports to formreaction beds. In a modern converter,there four reaction beds, eachconsisting of a layer of catalyst pelletsabout 0.6 m deep.

A conversion of 99.5 percent of sulfurdioxide to sulfur trioxide is essentialfor both economic and environmentalreasons. This can only be attained byremoving heat between reaction bedsand by removing the sulfur trioxideproduced between the third andfourth beds.

The mixture of gases that remain afterabsorption consists mostly of nitrogen,together with a small proportion ofoxygen and traces of sulfur dioxide.The gases are filtered to remove anysulfuric acid before being released intothe atmosphere at high level via astack.

Sulfuric acid is used in a wide varietyof industries. Important uses includethe manufacture of general chemicals,paints and pigments, detergents andsoaps, and phosphatic fertilizers.

86

Industrial preparation of sulfuric acid

SulfurSulfur

burning

Heatexchangers

SO2 + 02ReactorTemperature:

420–620°CPressure:

a littlemore thanatmosphere

Catalyst:vanadium(V) oxide

Water

Excessdry air

Absorbtion into98% sulfuric

acid

Dilution Waste gases95% nitrogen5% oxygen

sulfur dioxide

Product98%

sulfuric acid

99.5% sulfuricacid

SO3, S02 + depleted air

catalystoresulfidesulfursulfur dioxide

sulfuric acidsulfur trioxide

Key words


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Affinity of concentratedsulfuric acid for water

Reaction withatmospheric water

Reaction withsugar solution

H2O

H2SO4

H2O

H2O H2O

H2O

H2O H2OH2SO4

4 Forming esters and alkenes

R C

O

OH H OR1

R C

O

OR1

–H2O

Carboxylic acid Alcohol Ester

2 Illustrating sulfuric acid’s affinity for water

1 Sulfuric acid and atmospheric water

3 Drying gases

concentratedsulfuric acid

atmosphericwater

severaldayslater

steam

mass ofcarbon

sucrose

sulfuric acidadded

wetgas

drygas

concentratedsulfiric acid

1 Sulfuric acid andatmospheric water Concentrated sulfuric acid will absorb

water from the air. The level of liquid in a beaker

containing concentrated sulfuric acidrises as water is absorbed and the acidbecomes more dilute.

2 Sulfuric acid’s affinity for water Concentrated sulfuric acid will remove

the elements of water from organicchemicals such as sucrose (C12H22O11).

When concentrated sulfuric acid ispoured onto sucrose, the crystallinewhite sucrose turns into a blackamorphous mass of carbon.

3 Drying gases Concentrated sulfuric acid can be used

to dry gases, such as hydrogen. Thegas is bubbled through the acid in asuitable container.

Some gases, such as ammonia, reactwith concentrated sulfuric acid andcannot be dried in this way.

4 Forming esters andalkenes Concentrated sulfuric acid is used as a

catalyst in the formation of esters fromcarboxylic acids and alcohols.Concentrated sulfuric acid removesthe elements of water from alcohols toform alkenes:

-H2O

R-CH2-CH2OH R-CH=CH2

alcoholalkenecarboxylic acidcatalystester

sulfuric acid

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Oxygen and sulfur:oxidation and reduction


1 Common redox reactions Oxidation reactions and reduction

reactions are more accuratelydescribed as redox reactions becausethey cannot occur in isolation. Onesubstance is reduced and another isoxidized at the same time.

Hydrogen sulfide reduces chlorine gasto chloride ions. The sulfide isoxidized to elemental sulfur:Cl2 + 2e- 2Cl- reductionS2- S + 2e- oxidation

Hydrogen peroxide is an oxidizingagent but is itself oxidized by a morepowerful oxidizing agent such aspotassium manganate(VII).

Sulfur dioxide is a reducing agentboth in the gaseous form and inaqueous solution. It reduces iron(III)to iron(II) while being itself oxidizedto a sulfate:Fe3+ + e- Fe2+ reduction

Sulfur dioxide can be oxidized tosulfur trioxide by reaction with oxygen.

Copper reacts with concentratedsulfuric acid. In this reaction, theconcentrated sulfuric acid acts as anoxidizing agent, oxidizing coppermetal to copper(II). The sulfuric acidis itself reduced to sulfur dioxide:Cu Cu2+ + 2e- oxidation

2 Sulfuric acid and sulfatereactions Sulfuric acid reacts with metal oxides

to form sulfates and water. Sulfuric acid reacts with metal

hydroxides to form sulfates and water Sulfuric acid reacts with metal

carbonates to form salts, carbondioxide, and water

In all of these reactions, no oxidationor reduction takes place. The chargeon the metal ion in the oxide,hydroxide, and carbonate is the sameas it is in the sulfate.

88

Cu + 2H2SO4 CUSO4 + H2O + SO2Concentrated sulfuric acid oxidizes copper

→

O2 + 2SO2 2SO3Oxygen oxidizes sulfur dioxide

SO2 + 2FeCl3 + 2H2O 2FeCl2 + 2HCl + H2SO4Sulfur oxide reduces iron chloride solution

H2O2 + 3KMnO4 2KOH + 2MnO2 + 2O2Hydrogen peroxide reduces potassium manganate(VII) solution

8H2S + 8Cl2 S8 + 16HClHydrogen sulfide reduces chlorine gas

Acid + metal oxide = Salt + water

H2SO4 + MgO MgSO4 + H2O

H2SO4 + Cu(OH)2 CuSO4 + 2H2OAcid + metal hydroxide = Salt + water

H2SO4 + ZnCO3 ZnSO4 + CO2 + H2OAcid + metal carbonate = Salt + carbon dioxide + water

1 Common redox reactions

2 Sulfuric acid and sulfate reactions

hydrogenperoxide

hydrogensulfide

oxidizing agent

oxygenredox reactionreductionsulfursulfur dioxide

Key words


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Basic reactions ofoxygen

a oxidizes reactive metalsb accepts protons from acidsc gives protons to basesd reacts with non-metal oxides

1 Reactions

2H2 + O2 2H2O

2 The hydrides

4Na + O2 2Na2O

Oxidizes other elements

→

H2O2 + 2KMnO4 2KOH + 2MnO2 + 2O2

H2O4 + 2FeCl2 + 2HCl 2FeCl3 + 2H2O

ZnO + 2NaOH Na2Zn(CH)4 + H2O

a

b

c

d

g

h

j

k

e

f

i

e preparationf an oxiding agentg a reducing agenth basic

i amphotericj acidick neutral

2Na + O2 Na2O2

S8 + 8O2 8SO2

P4 + 5O2 P4O10

2Cu + O2 2CuO

2CO + O2 2CO2

2SO2 + O2 2SO3


4NH3 + 5O2 4NO + 6H2O

2Na + 2H2O 2NaOH + H2

Water

H2O + HCl H3O+ + Cl–

H2O + NH3 NH4+ + OH–

H2O + CO2 H2CO3

H2O + SO2 H2SO3

BaO2 + H2SO4 H2O2 + BaO4


CuO + H2SO4 CuSO4 + H2OZnO + H2SO4 ZnSO4 + H2O

SO2, CO2

H2O, CO



3 The oxides

→

1 Reactions Oxygen reacts with both metals and

non-metals to form oxides. Group 1 and group 2 metals often

form more than one oxide:Na2O sodium monoxideNa2O2 sodium peroxideNaO2 sodium dioxide

Transition metals form oxides inwhich the metal exhibits differentvalency states:Cu2O copper(I) oxideCuO copper(II) oxide

Non-metallic elements also form morethan one oxide:P4O6 phosphorus(III) oxideP4O10 phosphorus(V) oxide

2 The hydrides Water reacts with group 1 and group 2

metals to give the metal hydroxideand hydrogen. In these reactions, themetal is oxidized to a metal cation andthe water is reduced:M M+ and M M2+

In the Brønsted-Lowry theory of acidsand bases, an acid is defined as asubstance that donates protons and abase as a substance that acceptsprotons. Water acts as both an acidand a base.

Non-metallic oxides dissolve in waterto form acids:H2CO3 H+ + HCO3

- carbonic acidH2SO3 H+ + HSO3 sulfurous acid

3 The oxides Metal oxides are basic and react with

acids to form salts and water. Non-metallic oxides are acidic or

neutral. Some metal oxides are amphoteric:

they react with both acids and alkalis.

alkaliamphotericcationhydroxideoxide

oxygentransition metalsvalency

Key words

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Basic reactions of sulfurPATTERNS—NON-METALS

1 Reactions of sulfur Sulfur reacts with most metals and

hydrogen to form sulfides. Metalsulfides react with acids to givehydrogen sulfide:FeS(s) + 2HCl(aq)

FeCl2(aq) + H2S(g)

Sulfur combines with non-metals suchas oxygen and chlorine.

Sulfur dioxide is formed by thereaction between concentratedsulfuric acid and sulfur.

2 The hydrides Hydrogen sulfide dissolves in water to

form a weak acid. Group 1 metal sulfides are soluble in

water, however, other metal sulfidesare only sparingly soluble and formcharacteristically colored precipitates.Moist lead(II) ethanoate paper turnsblack in the presence of hydrogensulfide due to the formation of leadsulfide:Pb2+ + S2- PbS

Hydrogen sulfide and sulfur dioxideundergo a redox reaction to formelemental sulfur.

3 The oxides SO2 and SO3 Sulfur dioxide dissolves in water to

form sulfurous acid, a weak acid. Sulfur dioxide is oxidized to sulfur

trioxide. Sulfur trioxide dissolves in water to

form sulfuric acid, a strong acid.

4 The hydroxy compound Concentrated sulfuric acid is a strong

oxidizing agent and will oxidize bothmetals and non-metals.

Concentrated sulfuric acid is a strongdehyrating agent and will removewater or the elements of water.

90

1 Reactions of sulfurOxidizes some elements

Reduces other elements elements

Reduces some compounds

Fe + S FeS2Cu + S Cu2SH2 + S H2S

S + O2 SO22S + Cl2 S2Cl2

3S + 2H2SO4 3SO2 + 2H2O→

2 The hydridesIs a sparingly soluble acidic gas

CuSO4 + H2S CuS + H2SO4

→

2H2S + SO2 2H2O + 3S

→

H2S + H2O H3O+ + HS–

Is a reducing agent

Causes precipitation of insoluble metel sulfides

Is a sparingly soluble acidic gas

3 The oxides SO2 and SO3

SO3 is very acidic

2SO2 + O2 2SO3

SO3 + H2O H2SO4

SO2 + H2O H2SO3Is reducing agent

SO2 + 2H2S 3S + 2H2O

As a strong acid

As a dehydrating agent

As an oxidizing agent

4 The hydroxy compound

→→

H2SO4 + H2O H3O+ + HSO4

–

2H2SO4 + C CO2 + 2SO2 + 2H2OCu + 2H2SO4 CuSO4 + SO2 + 2H2O

CH3CH2OH CH2 = CH2H2SO4

170°C

C12H22O11 12CH2SO4

–11H2O

CuSO4.5H2O CuSO4H2SO4

–5H2O

→

dehydratingagent

hydrogen sulfideoxidizing agentredox reaction

sulfidesulfursulfur dioxidesulfuric acid

Key words


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The halogens: group 7

Halogens The elements of group 7 are

sometimes referred to as the halogens.They are flourine, chlorine, bromine,iodine, and astatine. The symbol ‘X’ isoften used to denote a halogen atomand ‘X-’ a halogen ion.

1 Electron structure All halogen atoms have seven

electrons in their outer shell. A halogen atom needs one moreelectron to fill the outer shell, and itcan obtain this either by forming asingle covalent bond or by forming anion, X-. Halogens form both covalentcompounds and ionic compounds.

2 Halogen atom andmolecule Halogens exist as diatomic molecules.

Each atom in the molecule provides asingle electron to form a covalentbond. The result is that each atom hascontrol over eight electrons.

3 Physical properties There is a gradation of physical

properties going down group 7.1. State changes from solid to liquid togas. Bromine is one of only twoelements that exist as liquids at roomtemperature.2. The color darkens from pale yellowto black.3. Melting point and boiling pointincrease.

There is a gradual decrease inchemical reactivity going downgroup 7.

Fluorine oxidizes water to give oxygen:2F2 + 2H2O 4HF + O2

Chlorine reacts less vigorously withwater, forming an acidic solution:C2 + H2O HCl + HOCl

Bromine and iodine form solutions inwater, although the latter is not verysoluble.

astatinebrominechlorinecovalent bondcovalent

compound

fluorinehalogensiodineionic compound

Key words

X

XX

2 Halogen atom and molecule

Element

State at 20°C

Color

m.p./°C

b.p./°C

Solubility/g per 100gof water at 20°C

Chlorine

Atomic number

Relative atomic mass

Fluorine Bromine Iodine

gas

pale yellow

–220

–188

reacts readilywith water

9

19.0

gas

pale green

–101

–35

0.59 (reactsslightly

17

35.5

liquid

red-brown

–7

59

3.6

35

79.9

solid

black

113

183

0.018

53

126.9

Halogen atom

Halogen molecule

1 Electron structure

F

Cl

Br

I 2

2

8

2

8

18

18

7

7

7

7

3 Physical properties

inner electrons outer shell

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Laboratory preparationof the halogens


1 Laboratory preparation of chlorine Chlorine is made in the laboratory by

the oxidation of concentratedhydrochloric acid using a suitableoxidizing agent such as manganesedioxide (manganese(IV) oxide):MnO2(s) + 4HCl(aq)

MnCl2(aq) + 2H2O(l) + Cl2(g)

The gas is first passed through waterto remove any hydrogen chloride gas,and then through concentratedsulfuric acid to dry the gas. Chlorine ismore dense than air and is collectedby downward delivery.

Chlorine can also be convenientlymade in the laboratory from bleachingpowder, using dilute hydrochloric acid:Ca(OCl)2(s) + 4HCl(aq)

CaCl2(aq) + 2H2O(l) + 2Cl2(g)

2 Laboratory preparation of bromine Bromine is made in a similar way to

chlorine:MnO2(s) + 2NaBr(aq) + 2H2SO4(aq)

MnSO4(aq) + Na2SO4(aq)

+ 2H2O(l) + Br2(g)

Because it boils at 59°C, bromine isremoved from the reaction mixture bydistillation.

3 Laboratory preparation of iodine Iodine is made in a similar way to

bromine. Hydrogen iodide is made insitu by reacting sodium iodide withconcentrated sulfuric acid:MnO2(s) + 2KI(aq) + 2H2SO4(aq)

MnSO4(aq) + K2SO4(aq) +

2H2O(l) + I2(g)

Iodine is removed from the reactionmixture by sublimation. On heating, itchanges directly from solid to vaporand then back to solid on cooling.

92

brominechlorinedistillationiodineoxidation

oxidizing agent

Key words

3 Laboratory preparation of iodine

1 Laboratory preparation of chlorine

2 Laboratory preparation of bromine

a concentrated hydrochloric acidb manganese dioxidec warm gentlyd water to remove HCl fumese concentrated H2SO4 to dry Cl2f chlorine gasg concentrated brineh chlorine gasi hydrogen gasj waterk concentrated sulfuric acidl manganese oxide + sodium bromidem warm gentlyp cold watero fumes of HBrp bromineq manganese oxide + potassium iodine

+ concentrated H2SO4s warm gentlyt cold water

a

b

c

d

k

l

m

n

o

p

r

s

t

q

e f


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Compounds of chlorine

1 Chlorine and metals Metals, such as calcium, burn in

chlorine to produce thecorresponding metal chloride:Ca(s) + Cl2(g) CaCl2(s)

Aluminum reacts with chlorine to formaluminum chloride:2Al(s) + 3Cl2(g) 2AlCl3(s)

Unlike many metal chlorides,aluminum chloride is hydrolyzed bywater, giving off hydrogen chloridegas:AlCl3(s) + 3H2O(l)

Al(OH)3(s) + 3HCl(g)

It is for this reason that aluminumhalides fume when they come intocontact with moist air.

2 Laboratory preparationof hydrogen chloride Hydrogen chloride is made by the

reaction of sodium chloride withconcentrated sulfuric acid:NaCl(s) + H2SO4(aq)

NaHSO4(s) + HCl(g)

3 Compounds with non-metals Chlorine forms covalent compounds

with non-metals such as carbon,phosphorus, and sulfur.

4 Pesticides Chlorinated compounds provide a

range of pesticides. DDT, BHC, Aldrin, and Dieldrin have

been the source of environmentalconcern, and their use is nowprohibited or severely restricted.

chloridechlorinecovalent

compoundhalide

hydrogenchloride

sodium chloridesulfuric acid

Key words

Benzene hexachloride (BHC) Aldrin Dieldrin

Dichlorophenyl-trichloroethane(DDT)

Calcium burnsin chlorine

Aluminum reacts whenwarmed in a stream ofchloride

2 Laboratory preparation of hydrogen chloride

3 Compounds with non-metals

ClHH H

Cl C CC

Cl

C C HH

Cl ClClH

C

ClCl

ClCl

CCl2C

CC

CC

CH

H

CH2

C

CH

H

CH

CH

ClCl

ClCl

CCl2C

CC

CC

CH

H

CH2

C

CH

H

CH

CH

O

C C Cl

Cl

Cl

C

CClC

ClC

CC

CC

CC

CC

HHH

HH

HH

HH4 The structure of somechlorinated pesticides

Cl Cl

Cl Cl

C

Cl

Cl

ClP

Cl

Cl

S S

Carbon tetrachloride (CCl4) Phosphorus trichloride (PCl3) Sulfur monochloride (S2Cl2)

chlorine

calcium

heat

chlorine

aluminum

white smoke

to fumecupboard

concentrated sulfuric acid

sodium chloride

hydrogen chloride

1 Chlorine and metals

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Hydrogen chloride in solution


Hydrogen chloride Hydrogen chloride gas is a covalent

compound. In solutions in organicsolvents, it remains a covalentcompound. It becomes an ioniccompound in aqueous solutions.

1 In organic solvents In solution in organic solvents such as

methylbenzene, hydrogen chlorideremains a covalent compound. Thehydrogen atom and the chlorine atomeach donate one electron to form thecovalent bond.

The solution contains no ions anddoes not conduct electricity.

The solution has no effect on bluelitmus paper or on carbonates, thusshowing that it is not an acid.

2 In aqueous solution In aqueous solution, hydrogen

chloride becomes an ionic compound.The hydrogen atom loses an electronto become a hydrogen ion, H+, andthe chlorine atom gains an electron tobecome a chloride ion, Cl-.

The solution contains ions andconducts electricity. The ions are ableto carry a charge through the solution.

The solution turns blue litmus paperred and reacts with carbonates,showing that it is an acid:Na2CO3(aq) + 2HCl(aq)

2NaCl(aq) + CO2(g) + H2O(l)

94

H–Cl

H–Cl

H–Cl

H–Cl

H–Cl

ClH

H+Cl–

ClH

H+Cl–

H+

Cl–

Cl–

H+

1 In organic solvents

2 In aqueous solution

carbonatecovalent bondcovalent

compoundhydrogen

chloride

ionionic compound

Key words


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Acid/base chemistry of the halogens

1 Laboratory preparation of hydrochloric acid

silver nitratesolution

2 Solubility of the halogens

Flouorine is so reactive it decomposes water producing hydrofluoric acid and oxygen

Chlorine is the next most reactive halogen after fluorine

3 Chloride test

solution

Dissolve unknown substance,adding dilute nitric acid tothe solution. Add a few dropsof silver nitrate solution

Colored precipitationproves presence ofchloride, bromide,or iodine

b

a

Hydrogen chloride enterswater via a filter funnel

The level in thebeaker drops

The cyclestarts again

a hydrochloric acid (HCl)b plug of liquid in funnel

2F2 + 2H2O 4HF + O2

Cl2 + H2O HCl + HOCl

a a1 Laboratory preparation ofhydrochloric acid Hydrochloric acid is made in the

laboratory by dissolving hydrogenchloride gas in water.

Hydrogen chloride is very soluble inwater. It is dissolved by passingthrough an inverted filter funnel, therim of which sits just below the waterlevel. When water is sucked into thefunnel, the water level drops, and thefunnel rim is no longer submerged.This prevents water being sucked backinto the apparatus.

2 Solubility of the halogens All halogens are oxidizing agents.

However, oxidizing power decreasesdown the group:fluorine > chlorine > bromine >

iodine Halide ions are reducing agents. The

reducing power increases down thegroup:fluorine < chlorine < bromine <

iodine

3 Chloride test The presence of halide ions in solution

can be detected by adding a few dropsof dilute nitric acid followed byseveral drops of silver nitrate solution.1. Chloride ions form a whiteprecipitate of insoluble silver chloride:Ag+(aq) + Cl-(aq) AgCl(s)

2. Bromide ions form a creamprecipitate of insoluble silver bromide:Ag+(aq) + Br-(aq) AgBr(s)

3. Iodide ions form a yellowprecipitate of insoluble silver iodide:Ag+(aq) + I-(aq) AgI(s)

halidehydrochloric acidhydrogen

chloridenitric acid

oxidizing agentreducing agentsilver nitrate

Key words

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Redox reactions of thehalogens


1 Calcium and chlorine When hydrogen sulfide and chlorine

are mixed, elemental sulfur is formed.Chlorine acts as an oxidizing agentand oxidizes the hydrogen sulfide byremoving hydrogen. In turn, thechlorine gains hydrogen and isreduced to hydrogen chloride:8H2S(g) + 8Cl2(g) S8(s) + 16HCl(g)

2 Chlorine and ferrouschloride Chlorine can also be used to oxidize

iron(II) to iron(III). When chlorine isbubbled into iron(II) chloride solution,the color changes from green toyellow-brown, showing the formationof iron(III). The chlorine atoms arereduced to chloride ions:2FeCl2(aq) + Cl2(g) 2FeCl3(aq)

3 Halogens and metals Halogens readily oxidize metals.

Fluorine oxidizes all metals, includinggold and silver, easily.

Chlorine oxidizes all but the leastreactive metals. When iron is heated ina stream of dry chlorine, iron(III)chloride is produced: 2Fe(s) + 3Cl2(g) 2FeCl3(s)

The ease with which halogens oxidizemetals decreases down the group, buteven iodine will slowly oxidize metalslow in the reactivity series.

4 Halogens and non-metals Fluorine oxidizes most non-metals

except nitrogen and most of the noblegases.

Chlorine reacts directly withphosphorus and sulfur, but carbon,nitrogen, and oxygen do not reactdirectly with chlorine, bromine, oriodine.

The relative reactivities of the halogensin redox reactions with non-metals isillustrated at right by their reactionwith hydrogen.

96

chloridechlorinenoble gasesoxidizing agentreactivity series

redox reactionsulfur

Key words

chlorine gas

iron(III) chloride

dry chlorine

heat

green iron chloridesolution

chlorine gas

plate

hydrogen sulfidegas

plate

sulfur coatinginside gas jars

1 Calcium burns in chlorine

3 Halogens and metals

4 Halogens and non-metals

Reaction

H2(g) + F2(g) → 2HF(g)

H2(g) + Cl2(g) → 2HCl(g)

H2(g) + Br2(g) → 2HBr(g)

H2(g) + I2(g) → 2Hl(g)

explosive

explosive in sunlight but slow in the dark

needs heat and a catalyst

slow even when heated

Observations

Chlorine gas and hydrogensulfide gas are separated

by plate

Plate is removed

2 Reaction of chlorine with ferrous chloride

Chlorine gas is passed intoferrous chloride solution

Yellow-brown ironchloride solution


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Reactivity of the halogens

1 Reactivity of halogens The chemical reactivity of the

halogens decreases down group 7:fluorine > chlorine > bromine >

iodine A more reactive halogen will displace

the ions of a less reactive halogenfrom a metal halide solution. This iscalled a displacement reaction.

Chlorine will displace bromide ionsand iodide ions from solution.

Bromine will displace iodide ions fromsolution.

In a displacement reaction, thehalogen acts as an oxidizing agent andis reduced while the halide ion isoxidized.

2 Chlorine and bromine Chlorine dissolves in the organic

solvent hexane to give a colorless orslightly green solution, depending onconcentration.

Hexane is immiscible with water.When the two liquids are mixed,hexane forms a layer above water.

When solutions of chlorine in hexaneand potassium bromide in water areshaken together, chlorine displacesbromide ions from the aqueoussolution. Bromine is more soluble inhexane than in water, and an orangelayer of bromine in hexane forms:2KBr + Cl2 2KCl + Br2

2Br- + Cl2 2Cl- + Br2

3 Chlorine and iodine When solutions of chlorine in hexane

and potassium iodide in water areshaken together, chlorine displacesiodide ions from the aqueous solution.Iodine is more soluble in hexane thanin water, and a pink-purple layer ofiodine in hexane forms:2KI + Cl2 2KCl + I22I- + Cl2 2Cl- + I2

displacementreaction

halidehalogensimmiscible

Key words1 Chemical reactivity of halogens with each other

3 Reaction of chlorine and iodine

colorless aqueoussolution containing

K+ and Cl– ions

Chloride

Bromide

Iodide

Chlorine Bromine Iodine

2 Reaction of chlorine and bromine

colorless solution ofchlorine in hexane

colorless aqueoussolution containingK+ and I– ions

shaking

pink/purple solutionof iodine in hexane

colorless aqueoussolution containing

K+ and Cl– ions

colorless solution ofchlorine in hexane

colorless aqueoussolution containingK+ and Br– ions

shaking

orange solution ofbromine in hexane

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World distribution of metals

PATTERNS—METALS

1 Gold, sliver, platinum,and uranium Gold: South Africa, USA, Canada,

Russia Silver: USA, South America Platinum: South Africa, USA, South

America Uranium: North America, Europe,

Central and South Africa, Australia

2 Aluminum and copper Aluminum: South America, Jamaica,

West Africa, Russia, India, Australia Copper: North America, Central and

South Africa, Europe, Russia

3 Iron, zinc, and lead Iron: North and South America,

Russia, Europe, Angola, Australia Zinc and lead: USA, Europe, Australia,

Russia

98

aluminumcoppergoldironlead

platinumsilveruraniumzinc

Key words

1 Gold, sliver, platinum, and uranium

2 Aluminum and copper

3 Iron, zinc, and lead

goldsilverplatinumuranium

ironzinc and lead

aluminumcopper

PATTERNS—METALS

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Main ores of metalsMetal Chemical name Formula of ore(s)Common name for ore(s)for ore(s)

aluminumbauxite aluminum oxide

chromiumchromite iron chromium oxide

copperchalcopyrite copper iron sulfidebornite copper iron sulfidechalcocite copper(I) sulfide

ironhaematite iron(III) oxidemagnetite iron(II)iron(III) oxide

leadgalena lead(II) sulfidecerussite lead(II) carbonateanglesite lead(II) sulfate

magnesiummagnesite magnesium carbonate

mercurycinnabar mercury sulfide

silverargentite silver sulfide

sodiumsalt sodium chloride

tincassiterite tin oxide

titaniumrutile titanium oxideilmenite iron titanium oxide

uraniumuraninite uranium oxide

zinczinc blende zinc sulfidecalamine zinc carbonate

Al2O3.2H2O

FeCr2O4

CuFeS2Cu5FeS4Cu2S

Fe2O3Fe3O4

PbSPbCO3PbSO4

MgCO3

HgS

Ag2S

NaCl

SnO2

TiO2FeTiO3

UO2

ZnSZnCO3

Ores An ore is a mineral from which a

metal (or non-metal) can be extracted. Metal ores are often metal oxides or

metal sulfides. A metal may be present in a range of

different minerals, but not all mineralswill be suitable sources of that metal.

Recovering ores To be appropriate for mining, an ore

must contain minerals that arevaluable and that are concentratedenough to be mined profitably. It mustalso be economically viable to extractthe ore from waste rock.

Mineral deposits that are economicallyrecoverable are called ore deposits.Not all mineral deposits are suitablefor recovery. Some may be too low ingrade (the concentration of the ore inthe rock) or technically impossible toextract.

Formation The process of ore formation is called

ore genesis. Ore genesis involves a variety of

geological, internal, hydrothermal,metamorphic, and surficial processes.

grademineraloreoxidesulfide

Key words

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The group 1 metalsPATTERNS—METALS

1 Position in periodic table The group 1 metals occupy the first

column of the periodic table.Historically, they were known as thealkali metals because they all reactwith water to give alkaline solutions.

The elements include lithium, sodium,potassium, rubidium, and cesium.Francium lies below cesium in theperiodic table. However, it is notconsidered when discussing the groupbecause it is radioactive, and little isknown of its chemistry.

2 Electron-shell structure The electrons surrounding the nucleus

of an atom are arranged in a series oforbitals, areas around the atom wherethere is a high probability of finding anelectron. Orbitals are grouped in aseries of shells (energy levels) at agradually increasing distance from thenucleus. Different orbitals havedifferent shapes: s orbitals arespherically symmetric; p orbitals pointin a particular direction; and d orbitalshave complicated shapes. Scientistsdescribe an atom by describing theorbital structure. Thus, as the tableindicates, sodium has 2s orbitals in thefirst shell, 2s and 6p orbitals in thesecond shell, and 1s orbital in thethird shell.

3 Physical properties Reading down the group, the melting

point decreases, the boiling pointincreases, the density increases, andthe hardness decreases.

100

3 Physical properties of group I elementscompared with a typical metal

Li

Na

K

Rb

Cs

1 Position in the periodic table

metal reactivity decreasesacross a period

2 Electron-shell structure

ConductivityΩ–1cm–1

Hardness/Moh

Density/g cm–3b.p./°Cm.p./°C

Group 1element

LithiumSodiumPotassiumRubidiumCesium

LiNaKRbCs

18098643929

1336883759700669

0.530.970.861.531.88

0.60.40.50.30.2

11700238001640091002000

Typical metal

Iron Fe 1530 3000 7860 4–5 11300

metal reactivity increasesdown the group

1s22s1

1s2 2s2 2p6 3s1

1s2 2s2 2p6 3s2 3p6 4s1

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s1

Li

Na

K

Rb

Cs

1s2energy level

type of orbital

number of electronsin orbital

alkali metalsboiling pointgroup 1melting pointorbital

radioactiveshell

Key words

PATTERNS—METALS

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1 Reaction of NaOH with HCl Group 1 hydroxides are alkalis.

They can be used to form salts byneutralizing them with acids in aprocess call titration. Sodium chlorideis made by neutralizing sodiumhydroxide with hydrochloric acid.NaOH + HCl NaCl + H2O

A given volume of sodium hydroxidesolution is put into a conical flask.

A few drops of an acid–base indicatorare added to the sodium hydroxidesolution. The indicator is a differentcolor in acids and alkalis.

Hydrochloric acid is run into thesodium hydroxide solution buretteuntil the indicator just changes color.

2 Burning sodium Sodium burns vigorously in chlorine to

form sodium chloride:2Na + Cl2 2NaCl

Sodium also burns vigorously inoxygen to form sodium oxide:4Na + O2 2Na2O

3 Sodium and nitrogen When heated in a stream of nitrogen,

sodium reacts to form sodium nitride:6Na + N2 2Na3N

4 Preparation of sodium Sodium is obtained by the electrolysis

of molten sodium chloride in a Downscell. Sodium is discharged at thenegative electrode (cathode):Na+ + e- Na

The product at the positive electrode(anode) is chlorine gas:2Cl- Cl2 + 2e-

acidacid-base

indicatoralkalianode

cathodeelectrolysissalttitration

Key words

circularcathode

chlorine gas

molten sodiumchloride

anode

1 Reaction of sodium hydroxide (NaOH)with hydrochloric acid (HCl)

2 Sodium burnsreadily in chlorineor oxygen

Sodium hydroxidesolution is placedin the beaker

Hydrochloric acidis introduced intothe sodiumhydroxide solution

Results of thereaction

sodiumhydroxidesolution

blueindicator

pipette

burette

Hydrochloricacid

sodium chlorideindicator turnsgreen

3 Sodium reacts with nitrogen gas

heat

sodium

nitrogen

4 Commercial preparation of sodium

liquid sodium

The group 1 metals:sodium

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The group 2 metalsPATTERNS—METALS

1 Position in periodic table The group 2 metals occupy the second

column of the periodic table. Theyinclude beryllium, magnesium, calcium,strontium, and barium. Radium, whichlies below barium, is not usuallyconsidered when discussing the groupbecause it is radioactive. Historically,group 2 metals were known as thealkaline earth metals because all butberyllium react with water to givealkaline solutions.

The atomic radius and, therefore, thesize of the atoms increases goingdown the group.

2 Electron-shell structure Scientists can describe an atom by

describing its electron-shell structure(see page 150).

All group 2 elements form ions bylosing two outer electrons. The energyneeded to do this is the sum of thefirst and second ionization energies,i.e., the energy needed to remove thefirst electron and the second electron.

Going down the group, there is anincrease in the number of orbitals ofelectrons. This affects the value of theionization energy in two ways: 1) thetwo outer electrons are further fromthe positively charged nucleus, and 2)there are more layers of electronsbetween the nucleus and the outerelectrons, which partially shields theouter electrons from the nucleus.Consequently, going down the group,less energy is needed to remove theouter two electrons, and the metalsbecome progressively more reactive.

3 Reactivity As with the group 1 metals, the

reactivity of the group 2 metalsincreases going down the group.

The group 2 metals have similarchemical properties as group 1 metals;however, the reactivity of group 2metals in the same period is less.

102

Li Be

Na Mg

K Ca

reactivity increasesgoing down a group

reactivity decreases goingacross a period

I II

2

3

4

1s22s2

1s2 2s2 2p6 3s2

1s2 2s2 2p6 3s2 3p6 4s2

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2

Be

Mg

Ca

Sr

Ba

Be

Mg

Ca

Sr

Ba

1 Position in the periodic table

3 Reactivity comparison with group I

2 Electron-shell structure

1s2energy level

type of orbital

number of electronsin orbital

alkaline earthmetals

group 2ion

ionization energyorbitalradioactivereactivity

Key words

PATTERNS—METALS

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1 Sodium and water Sodium reacts vigorously with water to

form sodium hydroxide solution (astrong alkali) and hydrogen gas.

2 Calcium and water Calcium reacts less vigorously with

water than sodium to form calciumhydroxide solution and hydrogen gas.

Calcium hydroxide is less soluble thansodium hydroxide and forms a weakalkali solution containing suspendedparticles of undissolved solid.

3 Rainwater Naturally occurring rainwater is always

weakly acidic because carbon dioxidefrom the air dissolves in it, formingweak carbonic acid, H2CO3.

4 Effect of rainfall What rain flows over rocks, group 2

metal compounds dissolve in it,resulting in water that containsdissolved solids.

Magnesium and calcium carbonatesare effectively insoluble in water, butthey react with rainwater, because it isacidic, to form solublehydrogencarbonates.

5 Ca(OH)2 test Limewater, an aqueous solution of

calcium hydroxide, is used to test forcarbon dioxide.

When carbon dioxide is bubbled intolimewater, it turns milky due to theformation of insoluble calciumcarbonate, CaCo3.

6 BaCl2 test The test solution is first acidified with

dilute hydrochloric acid, and a fewdrops of barium chloride solution arethen added. If the solution containssulfate ions, a white precipitate ofbarium sulfate is formed.

alkalicarbonic acidgroup 2hydrochloric acidinsoluble

limewatersoluble

Key words

Gas

Ca + 2H2O =Ca(OH)2 + H2 →

Suspension2Na + 2H2O =2Na(OH) + H2 →

Solution

A white suspensionis produced if thesolution containsa sulfate

Add barium chloridedissolved inhydrochloric acidto the knownsolution

CO2 + H2O = H2CO3CO2 gas

1 Sodium and water

bubbles

5 Calcium hydroxide[Ca(OH)2] test for carbondioxide gas

Bubble unknowngas into limewaterCa(OH2)

2 Calcium and water

pH = 7 pH = 7bubbles

pH = 10

milkysuspensionCaCO3

Result if thegas is CO2

6 Barium chloride (BaCl2)test for metal sulfates

3 Production of “rainwater”

Bubble unknowngas into limewaterCa(OH2)

Result if thegas is CO2 rocks with soluble group 2 compounds

(e.g., CaCl2, CaSO)

stream of water containingdissolved solids

limestonerocks

4 Effect of rainfall onfresh water

rain

pH = 12

The group 2 metals:general reactions

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The transition metals:electron structure

PATTERNS—METALS

Characteristics oftransition metals The transition metals are any of the

metallic elements with an incompleteinner electronic structure. While theoutermost shell contains at most twoelectrons, their next-to-outermostshells have incompletely filled orbitals,which fill up going across a period.The filling is not always regular.

The 40 transitional metals areorganized into four series: The firstseries, shown in the table, runs fromelement 21 (scandium) to element 30(zinc) and is in period 4. The secondseries, elements 39 (yttrium) to 48(cadmium), is in period 5. The third,elements 71 (lanthanum) to 80(mercury), is in period 6. The fourthseries, from 103 (lawrencium) to 112(ununbium), is the actinides andtransactinides.

Moving away from the nucleus,successive electron shells becomeprogressively closer in energy. Theenergy levels of the third and fourthorbitals are close in the first series oftransition metals.

The electronic structure of all of theelements in period 4 can be written asthat of the element argon togetherwith additional electrons filling the 3dand 4s orbitals (see table).

Transition metals often have coloredcompounds because their ions containelectrons in the 3d orbitals that canmove between energy levels, givingout light.

Transition metals tend to have hightensile strength (the maximum stress amaterial can withstand withoutbreaking), density, and melting andboiling points. They have a variety ofdifferent oxidation states and areoften good catalysts.

104

Table to show the electron structures of atoms and ions ofelements from scandium to zinc

(Ar) = electron structure of argon

Note: As the shells of electrons get further and further from the nucleus successive shellsbecome closer in energy

Element Symbol Electronic Common Electronicstructure ion structureof atom of ion

Scandium Sc (Ar)3d14s2 Sc3+ (Ar)

Titanium Ti (Ar)3d24s2 Ti4+ (Ar)

Vanadium V (Ar)3d34s2 V3+ (Ar)3d2

Chromium Cr (Ar)3d54s1 Cr3+ (Ar)3d3

Manganese Mn (Ar)3d54s2 Mn2+ (Ar)3d5

Iron Fe (Ar)3d64s2 Fe2+ (Ar)3d6

Fe3+ (Ar)3d5

Cobalt Co (Ar)3d74s2 Co2+ (Ar)3d7

Nickel Ni (Ar)3d84s2 Ni2+ (Ar)3d8

Copper Cu (Ar)3d104s1 Cu+ (Ar)3d10

Cu2+ (Ar)3d9

Zinc Zn (Ar)3d104s2 Zn2+ (Ar)3d10

actinidescatalystorbitaloxidation stateshell

tensile strengthtransition metals

Key words

PATTERNS—METALS

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2 Physical properties of the elements from scandium to zinc

1 Graphs showing the second and third ionization energies ofthe elements from scandium to zinc

KJm

ol–1

4000

3500

3000

2500

2000

1500

1000

500

third ionizationenergy

22 2620 24 28 32

Element Atomic m.p./°C b.p./°C Density/ Ionic radius/nmradius/nm gcm–3 M2+ M3+

Sc 0.16 1540 2730 3.0 0.081

Ti 0.15 1680 3260 4.5 0.090 0.076

V 0.14 1900 3400 6.1 0.088 0.074

Cr 0.13 1890 2480 7.2 0.084 0.069

Mn 0.14 1240 2100 7.4 0.080 0.066

Fe 0.13 1540 3000 7.9 0.076 0.064

Co 0.13 1500 2900 8.9 0.074 0.063

Ni 0.13 1450 2730 8.9 0.072 0.062

Cu 0.13 1080 2600 8.9 0.070

Zn 0.13 420 910 7.1 0.074

30

Cu

Zn

NiCo

FeMnCr

VTi

Sc

Sc

Tc

VCr

Mn

Fe

CoNi

Cu

Zn

Atomic number

second ionizationenergy

Scandium

Titanium

Vanadium

Chromium

Manganese

Iron

Cobalt

Nickel

Copper

Zinc

1 Ionization energies Ionization energy is the energy

needed to remove an electron from aneutral gaseous atom or ion againstthe attraction of the nucleus.

The second ionization energy is theenergy needed to go from M+ to M2+,(where M = metal), and the thirdionization energy is the energy neededto go from M2+ to M3+.

The second ionization energyincreases across period 4 becausethere is an increasing positive chargeon the nucleus of the ion, making itincreasingly more difficult to removethe second electron.

The third ionization energy for allelements is significantly higher thanthe second. Removal of the secondelectron results in a greater netdifference between the positive chargeon the nucleus of the ion and thenegative charge surrounding it, so itrequires more energy to remove athird electron.

2 Physical properties Like other metals, transition metals

are good conductors of both heat andelectricity.

The transition metals in general havehigher melting points and boilingpoints than groups 1 and 2 metals.

The atomic radii and ionic radii for theM2+ ion decrease across period 4because the increasing positive chargeon the nucleus of the atom and of theion provides a greater attraction forthe surrounding electrons.

boiling pointconductorionization energymelting pointtransition metals

Key words

The transition metals:ionization energies andphysical properties

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AluminumPATTERNS—METALS

1 Extraction Bauxite, the ore from which

aluminum is obtained, containsimpurities, principally iron(III) oxide(Fe2O3), that must be removed beforethe ore can be processed to obtainaluminum.

Aluminum oxide is an amphotericoxide (it reacts with both acids andalkalis). After grinding, the ore ismixed with an excess of sodiumhydroxide solution, forming sodiumtetrahydroxoaluminate(III) solution.

Iron(III) oxide and the otherimpurities remain undissolved in thesodium hydroxide solution and arefiltered off.

The filtrate, containing sodiumtetrahydroxoaluminate(III), istransferred into a precipitation tank,where the solution decomposes,giving a precipitate of pure solidaluminum oxide.

2 Manufacture Aluminum oxide is reduced by

electrolysis in a Hall-Hérault cell. For electrolysis to occur, the

electrolyte must be molten so that theions are mobile and able carry electriccharge. The electrolyte consists of asolution of aluminum oxide andmolten cryolite (a compound ofaluminum fluoride and sodiumfluoride).

Aluminum oxide dissociates in thecryolite solution, giving aluminumions, Al3+, and oxide ions, O2-.

Aluminum ions are reduced toaluminum metal, which is tapped offmolten from the bottom of the cell.Oxide ions are oxidized to oxygen.

The graphite anode readily reacts withthe oxygen produced to give carbondioxide. The graphite anode isgradually eaten away and must bereplaced at regular intervals.

106

Addition ofNaOH solution

a graphite anodesb solid crust of electrolytec molten electrolyte

(aluminum oxide dissolved in cryolite)

d molten aluminum oxidee tapping holef graphite lining to cell (cathode)g insulation

–

+

a

b

c

d

ge

f

a

2 The electrolytic manufacture of aluminum

Bauxite(impure Al2O3)

Grinder

Filter to removeFe2O3 and otherinsoluble matter

Reactor

Al(OH)3precipitate Filter to

obtain Al(OH)3

Solid Al(OH)3

Pure Al2O3

Heater todecompose

Al(OH)3

Seed crystals orcarbon dioxide

added

1 Extraction of pure aluminum oxide (Al2O3)acidalkalialuminumamphotericcryolite

electrolysiselectrolytefiltrateoreprecipitate

Key words

PATTERNS—METALS

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Iron: smelting

Impurity % impurityin pig iron

2 Table of impurities of pig iron

Carbon

Silicon

Sulfur

Phosphorus

Manganese

1 The blast furnace

3 to 5

1 to 2

0.05 to 0.10

0.05 to 1.5

0.5 to 1.0

burning coke acts asa reducing agent

molten iron

molten slag

molten ironoutlet

hot air

hot gasoutlet

iron ore, coke, and limestone

425°C

725°C

1,725°C

1,225°C

1 The blast furnace Iron ores such as hematite and

magnetite contain oxygen. To createpure iron, the ores are smelted in ablast furnace to remove the oxygen.

A charge of iron ore, limestone, andcoke is fed into the top of the furnace,and hot air is blown in toward thebottom through pipes called tuyeres.

The coke is used as a fuel, as areducing agent, and also to supplycarbon, which dissolves in the molteniron formed.

The limestone acts as a flux (cleaningagent), combining with acidicimpurities in the iron ore to form aliquid slag (the waste produce ofsmelting).

Molten iron falls to the bottom of thefurnace, where it is tapped.

Molten slag floats on the molten ironand is drawn off.

Hot gases (carbon monoxide, carbondioxide, sulfur dioxide, nitrogen, andunreacted oxygen) are removed at thetop of the furnace.

The conversion of iron oxide to iron isa reduction. The main reducing agentis carbon monoxide.

Iron oxide is reduced to iron bycarbon monoxide, which itself isoxidized to carbon dioxide.

The temperature inside the blastfurnace is sufficient to decomposelimestone into calcium oxide andcarbon dioxide. Calcium oxide thencombines with impurities such assilicon dioxide to form slag.

2 Impurities The iron that leaves the blast furnace

(called pig iron) contains a variableamount of impurities, includingcarbon, silicon, sulfur, phosphorus,and manganese.

fluxorereducing agentreductionslag

smelting

Key words

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The manufacture of steelPATTERNS—METALS

1 Basic oxygen process Steel is an alloy of iron, carbon, and

other metals and non-metals. In the basic oxygen process, the

furnace is charged with controlledamounts of steel scrap and molteniron from a blast furnace. An oxygenlance, cooled by circulating water, islowered into the furnace, and highpurity oxygen is injected into thevessel at twice the speed of sound.Impurities are readily oxidized. Molteniron is also oxidized.

With the exception of carbonmonoxide, the remaining oxides allreact with calcium oxide, which isadded during the oxygen blow, to forma slag.

The resulting steel is highly oxidizedand not suitable for casting. It isdeoxidized by adding controlledamounts of aluminum and silicon in aseparate reaction vessel. Additionalmetals and non-metals are added atthis point to make different types ofsteel.

2 Electric arc furnace The electric arc furnace process uses

only cold scrap metal. The furnace is acircular bath with a moveable roofthrough which carbon electrodes canbe raised or lowered as required.

Scrap steel is placed in the furnace,the roof closed, and the electrodeslowered into position. When a currentis passed, an arc forms between thescrap steel and the electrodes, and theheat generated melts the scrap steel.

Lime, fluorspar, and iron ore areadded, and these combine withimpurities forming a slag. When thesteel has reached the correctcomposition, the slag is poured off,and the steel is tapped from thefurnace.

108 a aaa aaaaaaa aCharging the converter Position during blowing

Discharging the slag Discharging the steel

1 Basic oxygen process

2 Electric arc furnace

compressed airenters here

tuyeres(pipes)

pig iron

power cables

swivel roof

furnace door

furnace

graphite electrodes

refractory lining

water-cooled furnace roof

water-cooled panels

refractory lining

tapping spout

steel scrap

alloyslag

Key words

PATTERNS—METALS

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Rusting

Tube A Tube B Tube C

No rust No rust Rust

1 Rust experiment

2 Chemical process

3 Rust prevention

Fe2O3.xH2O

(rust)

Fe

Fe2+

Fe(OH)2

2e–

2OH–+H2O + O2

12

+2e–

air

water film

iron (or steel)

cathodic area

electron flow

anodic area

dissolved oxygen

water

anhydrouscalciumchloride

oil

boiledwater

ironnail

magnesium blocks

air

Rusting Rusting is the result of a chemical cell

being formed on the surface of ironwhen it is in contact with water andoxygen from the air.

1 Rust experiment The experiment at left proves that

both water and oxygen are needed forrusting.

Tube A: When water is boiled, the air itcontains is expelled, and oil preventsany air redissolving in the water. Thenail is exposed to water but notoxygen and does not rust.

Tube B: Anhydrous calcium chlorideremoves moisture from the air. Thenail is exposed to oxygen but notwater and does not rust.

Tube C: The nail is exposed to bothwater and oxygen, and rust forms on it.

2 Chemical process Iron atoms are oxidized to form first

iron(II) ions, Fe2+, and then iron(III)ions, Fe3+, present in rust, Fe2O3.xH2O.

Oxygen is reduced and combined withwater to form hydroxide ions, OH-.

3 Rust prevention Most methods of rust prevention

involve stopping iron or, morecommonly, steel from coming intocontact with water and/or oxygen inair. These methods include painting,greasing, coating in plastic, coating inzinc (galvanizing), and coating in tin.

Sacrificial protection involves boltingblocks of a more reactive metal, suchas magnesium, to a steel structure.The magnesium will oxidize morereadily than the iron and will thus“sacrifice itself ” in order to preventiron from rusting.

galvanizinghydroxide ionironmagnesiumrust

Key words

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Copper smelting andconverting

PATTERNS—METALS

1 Matte smelting Matte smelting is used to produce a

liquid sulfide phase (matte) containingas much copper as possible, and animmiscible liquid slag, which containsvirtually no copper.

Copper sulfide ores, such aschalcopyrite (CuFeS2) are mixed withsand and blown into the flash furnace:4CuFeS2(s) + 5O2(g) + 2SiO2(s)

2Cu2S.FeS(l) + 2FeSiO3(l) + 4SO2(g)

matte slag As the iron content of the matte falls

to about 1 percent, copper starts toform. This product is called “blistercopper” and is 98–99.5 percent pure.It is porous and brittle and requiresfurther refining to be commerciallyuseful.

Blister copper is melted to drive offsulfur dioxide, and air is blownthrough it to remove any sulfur. Theimpure copper is cast into anodes forelectro-refining.

2 Electro-refining In electro-refining, a large impure

copper anode and a small pure coppercathode are suspended in anelectrolyte consisting of copper(II)sulfate solution and sulfuric acid.

At the anode, copper atoms areoxidized to copper ions and pass intosolution. The anode graduallybecomes smaller:Cu(s) Cu2+(aq) + 2e-

At the cathode, copper ions areremoved from solution as they arereduced to copper atoms. The cathodegradually becomes larger: Cu2+(aq) + 2e- Cu(s)

Impurities that are insoluble in theelectrolyte fall to the bottom of thecell. These may include gold, silver,platinum, and tin, and in somecircumstances may be more valuablethan the copper produced.

110

matte

1 Matte smelting

2 Electro-refining

sand and oreconcentrate

oxygen

slag matte

gas exit

slag

oxygen

sand and oreconcentrate

impurities (including gold,silver, platinum, and tin)

impurecopperanode

purecopper

cathode

solution ofcopper (II)sulfate and

sulfuric acid

cathodeanode+ –

anodecathodeelectrolyteslag

Key words

PATTERNS—METALS

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Reactions of copper

doubly ionized copper

Concentrated nitricor sulfuric acid

DissolvedH+ (aq)

Dilute acids

Cu2+

CuO

CuCO3.Cu(OH)2

CuCl2

black copperoxide

brown copper chloride

CuCl

red, insolublecopper oxide

Cu2O

green patina white,insolublecopperchloride

Dilutestrongacids

no reaction

ConcentratedhydrochloricacidAir

(slowtarnishing)

Heatin drychlorine

Cu Heat in airat 800°C

Heat in airabove 1,000°C

Reactions of copper Copper is a transition metal. Its

normal oxidation state is copper(II),Cu2+, but it also forms some copper(I),Cu+, compounds. Copper is a relativelyunreactive metal. It does not reactwith dilute strong acids, water, orsteam.

When heated in air at 800°C, copper isoxidized to black copper(II) oxide:2Cu(s) + O2(g) 2CuO(s)

At temperatures over 1,000°C, redcopper(I) oxide is formed:4Cu(s) + O2(g) 2Cu2O(s)

Both oxides react with dilute acids toform copper(II) salts.

When heated in chlorine, copperforms brown copper(II) chloride.Cu(s) + Cl2(g) CuCl2(s)

White copper(I) chloride also existsand can be made by strongly heatingcopper(II) chloride:2CuCl2(s) 2CuCl(s) + Cl2(g)

It is also formed by the reaction ofcopper(II) oxide with concentratedhydrochloric acid via an complex ion,[CuCl2]-. When a solution containingthis ion is poured into water,copper(I) chloride is precipitated.

Copper tarnishes slowly in air, formingbasic copper(II) carbonate, acompound of copper(II) carbonate,and copper(II) hydroxide,CuCO3.Cu(OH)2. It is this compoundthat produces the green coloration,referred to as patina, on weatheredcopper.

Copper reacts with both concentratednitric and concentrated sulfuric acid.Both of these concentrated acids arepowerful oxidizing agents and reactwith copper in a different way than adilute acid reacts with a metal. Copperdoes not react with dilute acids.With concentrated sulfuric acid:Cu(s) + 2H2SO4(l)

CuSO4(aq) + 2H2O(l) + SO2(g)

With concentrated nitric acid:Cu(s) + 4HNO3

Cu(NO3)2(aq) + 2H2O(l) + 2NO2(g)

hydrochloric acidnitric acidoxidation stateoxidizing agent

sulfuric acidtransition metals

Key words

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Reaction summary:aluminum, iron, andcopper

PATTERNS—METALS

Reactivity Aluminum is the most reactive and

copper is least reactive of the threemetals.

All three metals react directly withnon-metals.

Oxides Aluminum has one oxide, Al2O3, which

is amphoteric and thus reacts withboth acids and alkalis. Iron has threeoxides: FeO, Fe2O3, and Fe3O4. Copperhas two: Cu2O and CuO. All metaloxides react with dilute acids to formsalts and water.

Hydroxides Aluminum hydroxide, like aluminum

oxide, is amphoteric. Iron forms twohydroxides by the addition of sodiumhydroxide solution to solutions of itssalts. Iron(II) salts produce a dirtygreen precipitate of iron(II) hydroxide,while iron(III) salts produce a red-brown precipitate of iron(III)hydroxide. Copper(II) hydroxideforms as a blue precipitate whensodium hydroxide is added to asolution of a copper salt.

All metal hydroxides react with alkalisto give metal salts and water.

Carbonates Aluminum and iron(III) do not form

carbonates. Iron(II) carbonate andcopper(II) carbonate decompose onheating to the corresponding metaloxide with the loss of carbon dioxidegas. The carbonates also react withdilute acids to forms metal salts,carbon dioxide, and water.

Valency Aluminum is in group 3 of the periodic

table and exhibits only one oxidationstate, +3, in its compounds. Iron andcopper are both transition metals andexhibit two oxidation states in theircompounds.

112

Aluminum

Preparation

Reaction of elements

Oxide

Hydroxide

Carbonate

Change of valency

Electrolysis of aluminum oxide

Al3+ + 3e– → Al at cathode

4Al + 3O2 → 2Al2O3 oxide layer formed

2Al + 3Cl2 → Al2Cl62Al + 3H2SO4 → Al2(SO4)3 + 3H2

Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O

Al2O3(s) + 2NaOH(aq) → Na[Al(OH)4](aq)

AlCl3 + 3NaOH → Al(OH)3 + 3NaCl

Al(OH)3 + 3HCl → AlCl3 + 3H2O

Al(OH)3(s) + NaOH(aq) → 2Na[Al(OH)4](aq) (amphoteric)

Only on oxidation

Not formed

Iron

Preparation


Oxide

Hydroxide

Carbonate

Change of valency

Chemical reduction in blast furnace

Fe2O3 + 3CO → 2Fe + 3CO2

2Fe + 2H2O + O2 → 2Fe(OH)2 rust

Fe + 2HCl → FeCl2 + H2

2Fe + 3Cl2 → 2FeCl3Fe + S → FeS

Fe + H2SO4 → FeSO4 + H2

FeO + H2SO4 → FeSO4 + H2O

Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O

FeCl2 + 2NaOH → Fe(OH)2 + 2NaCl

FeCl3 + 3NaOH → Fe(OH)3 + 3NaCl

Fe(OH)2 + 2HCl → FeCl2 + 2H2O

Fe(OH)3 + 3HCl → FeCl3 + 3H2O

2Fe2+(aq) + Cl2(g) → 2Fe3+

(aq) + 2Cl–(aq)

Unstable to heat. FeCO3 → FeO + CO2

FeCO3 + H2SO4 → FeSO4 + CO2 + H2O

Copper

Preparation


Oxide

Hydroxide

Carbonate

Change of valency

Thermal decomposition in furnace

Cu2S → 2Cu + SO2

2Cu + O2 → 2CuO

Cu + Cl2 → CuCl22Cu + S → Cu2S

CuCl2 + H2SO4 → no reaction with dilute acid

Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O with conc. acid

CuO + H2SO4 → CuSO4 + H2O

CuCl2 + 2NaOH → Cu(OH)2 + 2NaCl

Cu(OH)2 + 2HCl → CuCl2 + 2H2O

2Cu2+(aq) + 2l–(aq) → 2Cu+

(aq) + l2(s) then Cu+(aq) + l–(aq) → Cul(s)

Unstable to heat. CuCO3 → CuO + CO2

CuCO3 + H2SO4 → CuSO4 + CO2 + H2O

air

aluminumamphotericcarbonatecopperhydroxide

ironoxidation stateoxidetransition metalsvalency

Key words

PATTERNS—METALS

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The extraction of metalsfrom their oresMetal (Date of discovery)Ranked from highest tolowest in reactivity series

Sodium (1807)

Group 1

Magnesium (1808)

Group 2

Aluminum (1827)

Group 3

Zinc (1746)

Transition metal

Iron (ancient)

Transition metal

Tin (ancient)

Group 4

Lead (ancient)

Group 4

Copper (ancient)

Transition metal

Mercury (ancient)

Transition metal

Main ore from whichit is obtained

Rock salt

NaCl

Magnesite

MgCO3 and Mg2+

ions in seawater

Bauxite

Al2O3.2H2O

Zinc blende

ZnS

Hematite

Fe2O3

Tinstone

SnO2

Galena

PbS

Copper pyrites

CuFeS2

(CuS + FeS)

Cinnabar

HgS

Main method ofextraction

Electrolysis of

molten NaCl

Electrolysis of

molten MgCl2

Electrolysis of Al2O3

in molten cryolite

(Na3AIF6)

Heat sulfide in air

oxide. Dissolve oxide

in H2SO4, electrolyze

Reduce Fe2O3 with

carbon monoxide

Reduce SnO2 with

carbon

Heat sulfide in air

oxide. Reduce oxide

with carbon

Controlled heating

with correct amount

of air Cu + SO2

Heat in air

Hg + SO2

Extraction of metals The ease with which a metal is

obtained from its ore is directly relatedto its position in the reactivity seriesof metals.

Electrolytic reduction All of the group 1 and group 2 metals

and aluminum from group 3 arereactive metals and in the upper halfof the reactivity series. They cannot beobtained from their ores by chemicalreduction, i.e., by heating the ore witha reducing agent such as carbonmonoxide or carbon. These metals canonly be obtained by electrolyticreduction or electrolysis.

Consequently, it was impossible toobtain these metals before thediscovery and development ofelectricity at the end of the eighteenthcentury. All of these metals were firstmade in the early years of thenineteenth century, several by Englishchemist Sir Humphrey Davy.

Heating Zinc oxide and iron oxide are reduced

by heating with carbon monoxide.Although zinc can be obtained bychemical reduction, approximately 80percent of the world’s annualproduction is, in fact, obtained byelectrolysis.

All of the metals from iron and belowin the reactivity series are relativelyeasy to obtain from their ores byheating.

Iron is obtained by reduction withcarbon monoxide

Tin is obtained by reduction withcarbon

Lead is obtained by heating leadsulfide in air to produce an oxide,which is then reduced with carbon.

Copper is obtained by controlledheating with the correct amount of air

Mercury is obtained by heating in air.

electrolysisorereactivity seriesreduction

Key words

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Reactivity summary:metals

PATTERNS—METALS

Reactivity summary Metals can be arranged in

order of their reactivity,starting with the most reactive.This is called the reactivityseries. The relative reactivity ofmetals is reflected through allof their chemistry.

Reaction with oxygen Metals at the top of the

reactivity series readily burn inoxygen. Less reactive metals donot burn but form a surfacelayer of oxide. Metals at thebottom of the reactivity seriesare not oxidized byatmospheric oxygen.

Reaction with coldwater Metals at the top of the

reactivity series react readilywith cold water but withdecreasing vigor down tomagnesium. The metals belowmagnesium do not react withcold water.

Reaction with steam Metals react more vigorously

with steam than with coldwater. All of the metals downto iron react with steam withdecreasing vigor. The metalsbelow iron do not react withsteam.

Reaction with diluteacid All of the metals down to lead

react with dilute acids, withdecreasing vigor. The metalsbelow lead do not react withdilute acids.

114

Reaction with O2(g)on heating

Heat evolved whenmetal reacts with 1mole of O2 to formoxide shown /kJ

Reaction withcold water

Reaction withsteam

Reaction withdilute acid

Ca Mg Al Zn FeK Na Pb Cu Hg Ag Pt Au

form oxides(e.g.,Na2O) inlimited suppliesof O2, butperoxides(e.g., Na2O2)with excess O2

burn withdecreasingvigor toform oxides

do not burn,but onlyform a surfacelayer of oxide

do not burnor oxidizeon surface

CaCaO

MgMgO

AlAl2O3

ZnZnO

FeFe2O3

PbPbO

CuCuO

HgHgO

NaNa2O

AgAg2O

AuAu2O3

1272

1204

1114

697

548

436

311

182

832

61

54

do not displaceH2(g) fromcold water

KK2O 723

displace H2(g)from cold waterwith decreasingreactivityK, violently

displace H2(g)from cold waterwith decreasingreactivityMg, very slowly

do not displaceH2(g) fromcold water

do not displaceH2(g) fromdilute acid

do not displaceH2(g) fromdilute acid

displace H2(g)from diluteacid withdecreasing vigorK, explosively

Mg,very vigorousFe,steadily

Pb, very slowly

displace H2(g)from steam withdecreasing vigorK, very violently

displace H2(g)from steam withdecreasing vigorFe, very slowly)

do not displaceH2(g) from steam

do not displaceH2(g) from steam

Pt— —

oxidereactivityreactivity series

Key words

PATTERNS—METALS

115

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Tests on metals: flame test

Color of flame Likely ion present Metal

Apple green

Blue-green

Brick red

Crimson

Lilac

Orange-yellow

Red

Ba2+

Cu2+

Ca2+

Sr2+

K+

Na+

Li+

barium

copper

calcium

strontium

potassium

sodium

lithium

sample

flamecolor

platinum or nichrome wire

1 Flame test

2 Table of flame coloration

1 Flame test Several metal ions produce

characteristic colors when introducedto a bunsen flame either as a solid oras a solution of a salt.

A clean platinum or nichrome wire isdipped in concentrated hydrochloricacid and then into the solid orsolution.

The sample is introduced to themiddle of a non-luminous bunsenflame.

2 Flame coloration The following metals produce the

following colors in the flame test:barium: apple greencalcium: brick redcopper: blue-greenlithium: redpotassium: lilacsodium: orange-yellowstrontium: crimson

The lilac color of potassium issometimes difficult to see and is betterobserved through blue glass thatmakes the flame appear purple.

The orange-yellow color of sodium isvery intense and may mask the colorof other metal ions present.

ionsaltsolution

Key words

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Tests on metals: metal hydroxides

PATTERNS—METALS

1 Producing the hydroxide Group 1 metal hydroxides are very

soluble and form strong alkalinesolutions. Group 2 metal hydroxidesare less soluble but still dissolvesufficiently to form weak alkalinesolutions. All other metals forminsoluble hydroxides. If several dropsof sodium hydroxide (NaOH) solutionare added to a solution of a metal salt,a precipitate, often gelatinous, isformed. Care must be taken whencarrying out this reaction becausesome metals form precipitates thatredissolve in excess sodium hydroxidesolution. If sodium hydroxide solutionis added too quickly, the initialprecipitate may not be seen.

2 The reactions The reactions of metal salt solutions

with sodium hydroxide solution can beused to identify the metal.

Aluminum, zinc, and lead hydroxidesare all amphoteric. When sodiumhydroxide solution is added tosolutions of salts of these metals, aninitial white precipitate is formed.However, if excess sodium hydroxidesolution is added, the precipitatedissolves, forming a solution of asoluble complex compound. Al(OH)3(s) + NaOH(aq)

Na[Al(OH)4](aq)

sodium tetrahydroxoaluminate(III)

Zn(OH)2(s) + 2NaOH(aq)

Na2[Zn(OH)4](aq)

sodium tetrahydroxozincate(II)

Pb(OH)2(s) + 2NaOH(aq)

Na2[Pb(OH)4](aq)

sodium tetrahydroxoplumbate(II). Iron and copper are transition metals

and form characteristic coloredprecipitates with sodium hydroxidesolution.

116

Aluminum nitrate → white precipitate of aluminum hydroxideAl(NO3)3 + 3NaOH → 3NaNO3 + Al(OH)3 ↓

Zinc nitrate → white precipitate of zinc hydroxideZn(NO3)2 + 2NaOH → 2NaNO3 + Zn(OH)2 ↓

Lead nitrate → white precipitate of lead hydroxidePb(NO3)2 + 2NaOH → 2NaNO3 + Pb(OH)2 ↓

Iron(II) nitrate → green precipitate of iron(II) hydroxide

Fe(NO3)2 + 2NaOH → 2NaNO3 + Fe(OH)2 ↓

Iron(III) nitrate → rust-brown precipitate of iron(III) hydroxide

Fe(NO3)3 + 3NaOH → 3NaNO3 + Fe(OH)3 ↓

Copper nitrate → royal blue precipitate of copper hydroxideCu(NO3)2 + 2NaOH → 2NaNO3 + Cu(OH)2 ↓

2 The reactions

1 Producing the hydroxide from the metallic salt

Add a small amount of NaOHto metal salt solution

A jelly-like solid forms

a few drops of NaOH

metal saltsolution insoluble metal

hydroxide

amphoterichydroxideprecipitatesaltsodium hydroxide

transition metals

Key words

PATTERNS—METALS

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Tests on metals: metal ions

Barium

Alumnum

Copper

Iron(II)

Iron(III)

Lead

Silver

Zinc

To the test solutionMetal ion in solution Positive result

Add 1 or 2 drops of litmus solutionfollowed by dilute hydrochloric aciduntil the mixture is just acidic. Thenadd ammonia solution until justalkaline.

Blue lake – a gelatinous precipitateof aluminum hydroxide – is formed,and this absorbs the litmus, leavingthe solution almost colorless.

Add several drops of potassiumchromate solution.

A yellow precipitate of bariumchromate. Lead ions also give a yellowprecipitate, but lead chromate isdeeper yellow and turns orange onheating.

Add ammonia solution drop by dropuntil it is in excess.

An initial blue precipitate of copper(II)hydroxide that dissolves in excessammonia solution to give a deep bluesolution containing the complex ion[Cu(NH3)4]2+.

Add several drops of potassiumhexacyanoferrate(III) solution.

A deep blue solution is formed.

Add several drops of ammoniumthiocyanate solution.

Deep blood-red coloration.

Add several drops of potassium iodidesolution.

A yellow precipitate of lead(II) iodide.

Add several drops of potassiumchromate solution.

A brick-red precipitate of silverchromate.

Add ammonium chloride andammonia solution, then pass hydrogensulfide through the mixture.

A white, or more often dirty white,precipitate of zinc sulfide.

hydroxidereagent

Key words

Reacations with reagents

In addition to flame tests and the

properties of their hydroxides,

the presence of some metal ions in

solution can be demonstrated by their

reactions with particular reagents.

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Uses of metalsPATTERNS—METALS

Uses of metals The uses of metals are related to both

their physical and chemical properties.The physical properties of a metal aresometimes altered by mixing it withother metals or non-metals to formalloys.

Aluminum Aluminum has a low density but is too

soft for many applications. It isfrequently used as duralumin (an alloyof aluminum and copper) as astructural material in the manufactureof airplanes.

Zinc Zinc is above iron in the reactivity

series. During galvanizing, iron isdipped in molten zinc, and the layer ofzinc formed on the iron protects itfrom rusting. If the galvanized iron isscratched, exposing the iron, anelectrolytic cell forms between theiron and zinc, and the zinc corrodes inpreference to the iron.

Iron Iron is used for all sorts of structures,

most often as steel (an alloy of ironand carbon). The one serious problemwith iron and steel is that they rust onexposure to water and oxygen in theair.

Lead Lead has a high density and is

impervious to water, so it used asflashing on roofs. It is also used as inthe manufacture of car batteries. Inthe past, before its toxic nature wasunderstood, lead was also used forwater pipes and in paints. Solder (analloy of lead and tin) is widely used tojoin copper wires and copper pipes.

118

Strong but light; oxidelayer preventscorrosion.Light, but goodconductor.

Structural material forships, planes, cars,cookwareElectric cables

Reactive — givessacrificial protectionto iron; does notcorrode easily.Modifies theproperties of the otherelements.

Coating (galvanizing)steel

Alloys:brass (Zn/Cu)bronze (Zn/Sn/Cu)

Strong and cheap;properties can bemade suitable byalloying.

Structural material forall industries (in theform of steel)

Very malleable anddoes not corrode.Design of batterymakes rechargingpossible.Low melting point.

RoofingCar batteries

Solder (Pb/Sn alloy)

Very good conductor.Very ductile, does notcorrode easily.

Electric cablesPipesAlloys (see above)Coins (alloyed withnickel)

Metal Use Reason

Aluminum

Zinc

Iron

Lead

Copper

BATTERY

alloyaluminumcopperductilegalvanizing

ironleadreactivity serieszinc

Key words

Copper

Copper is very ductile and can be easily

drawn into wires. It is a good conductor of

electricity and is used for the conducting

parts of electric cables. Copper does not

react with water and is a good conductor

of heat. It is used for water pipes and

radiators.

CHEMICAL REACTIONS

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Reactivity of metals 1

1 Forming oxides andchlorides Most metals react with air to form

metal oxides. Reactive metals likemagnesium burn, producing light andheat. Less reactive metals like coppersimply change color on heating:2Mg(s) + O2(g) 2MgO(s)

2Cu(s) + O2 2CuO(s)

Metals will also form chlorides whenheated in chlorine:Mg(s) + Cl2(g) MgCl2(s)

Cu(s) + Cl2 CuCl2(s)

2 Forming hydroxides Very reactive metals like calcium and

sodium react with water to formsolutions of metal hydroxides andhydrogen gas:Ca(s) + 2H2O(l)

Ca(OH)2(aq) + H2(g)

2Na(s) + 2H2O(l)

2NaOH(aq) + H2(g)

Calcium hydroxide is less soluble inwater and forms a weak alkali.

Sodium hydroxide is very soluble inwater and forms a strong alkali.

3 Less reactive metals Less reactive metals, which react with

water very slowly or not at all, reactwith steam to form metal oxides andhydrogen gas.

Magnesium reacts very slowly withwater but readily with steam:Mg(s) + H2O(g) MgO(s) + H2(g)

Iron does not react with water butreacts with steam to form iron(II)diiron(III) oxide:3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)

The least reactive metals, such ascopper, do not react with water orsteam.

alkalicalciumchloridecopperiron

hydroxidemagnesiumoxidesodium

Key words

119

1 Forming oxides and chlorides

2 Forming hydroxides

3 Less reactive metals

a

b

c

d

g

h

j k

l

e

f

i

l

a oxygen or chlorineb burning piece of reactive metal

c calciumd cold watere inverted filter funnelf hydrogen

g waterh safety tubei steamj magnesium ribbonk hydrogen ignitesl heat

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Reactivity of metals 2CHEMICAL REACTIONS

1 Metal compounds The oxides of metals that are low in

the reactivity series, like copper, canbe reduced by heating them in astream of hydrogen gas.

All group 1 metal carbonates, with theexception of lithium carbonate, are notdecomposed on heating. All othermetal carbonates decompose onheating, forming the metal oxide andcarbon dioxide gas:Li2CO3(s) Li2O(s) + CO2(g)

MgCO3(s) MgO(s) + CO2(g)

CuCO3(s) CuO(s) + CO2(g)

Carbon dioxide gas is more dense thanair and can be poured from one testtube into another. Carbon dioxideturns limewater milky.

2 Generating electriccurrent When rods of zinc and copper are

placed in dilute sulfuric acid, a simpleelectrical cell is formed, and there is apotential voltage difference betweenthe two metals. If the two metals areconnected externally, electric currentflows.

The zinc rod becomes the positiveelectrode (anode) of the cell. Zincatoms are oxidized to form zinc ions:Zn(s) Zn2+(aq) + 2e-

The copper rod becomes the negativeelectrode (cathode) of the cell.Hydrogen ions are reduced tohydrogen gas:2H+(aq) + 2e- H2(g)

If the copper rod is surrounded by aporous vessel containing copper(II)sulfate solution, a different reactionoccurs at the cathode:Cu2+(aq) + 2e- Cu(s)

Zinc atoms are oxidized to zinc ions,while copper ions are reduced tocopper atoms.

120

anodecarbonatecathodelimewateroxide

reactivity seriessulfuric acid

Key words1 Reactions of metal compounds

a

b c d

g

h j

k

e

f

i

l

k zinc rodl electric bulbm electron transfern connecting wireo copper rodp beakerq dilute sulfuric acid

2 Generation of electric current by mechanical reaction

Reduction of oxides

g

Effect of heat on carbonate

mn

o

p

s

u

t

q

v

r

Method 1: simple cell

Method 2r copper rods zinc rodt porous vesselu dilute sulfuric acidv copper sulfate solution

a hydrogenb combustion tube clamped to

slope downwardc metallic oxided porcelain vessele moisture collects heref hydrogen ignitedg heat

h metallic carbonatei carbon dioxidej limewater

CHEMICAL REACTIONS

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Electrolysis

1 Electrolysis Electrolysis is the process by which an

electrolyte (a substance that conductselectricity) is decomposed when adirect current is passed through itbetween electrodes. Positive cationsmove to the cathode to gain electrons;negative anions move to the anode tolose electrons.

Substances are either deposited orliberated at the electrodes dependingon the nature of the electrodes andelectrolyte.

2 Salt solutions Two electrolytes undergo electrolysis

at the same time when they areconnected in a circuit by a salt bridge.

The platinum electrode in the left-hand beaker is the anode and attractsnegative ions, which are oxidized.

The platinum electrode in the right-hand beaker is the cathode andattracts positive ions, which arereduced.

3 Water The electrolysis of water yields

hydrogen at the cathode and oxygenat the anode. Hydrogen and oxygenare formed in the ratio of 2:1.

4 U tube The ions present in dilute sulfuric acid

are H+, OH-, and SO42-. Hydroxide ions

are discharged at the anode, leaving asurplus of hydrogen ions, so theelectrolyte in the left side of the Utube becomes increasingly acidic.

The ions present in sodium sulfatesolution are H+, Na+, OH-, and SO4

2-.Hydrogen ions are discharged at thecathode, leaving a surplus ofhydroxide ions, so the electrolyte inthe right side of the U tube becomesincreasingly alkaline.

anionanodecathodecationelectrode

electrolysiselectrolyte

Key words

+ –

+–

1 Electrolysis: schematic

l

n

o

a batteryb electric bulbc liquid under testd poly(ethene) supporte copper platesf glass vesselg platinum electrodesh electrolyte solution in beakersi salt bridge

j platinum cathodek platinum anodel hydrogenm oxygenn water acidified with dilute sulfuric acido dilute sulfuric acidp agar jelly colored pink by phenolphthalein

and alkaliq sodium sulfate solution

2 Electrolysis of saltsolutions

3 Electrolysis of water 4 U tube

m

a

b

c

d

j k

p

q

e

f

h

i

g g

h

n

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CHEMICAL REACTIONS

Electrode activity andconcentration The results of electrolysis differ

depending on the concentration of thesolution and type of electrodes used.

Inert electrodes take no part in thereaction; active electrodes take part inthe reaction.

1 Dilute solution Reaction at the anode: oxygen

produced Reaction at the cathode: hydrogen

produced

2 Concentrated solution Reaction at the anode: chlorine

produced Reaction at the cathode: hydrogen

produced

3 Inert electrodes The following reactions occur at the

electrodes when copper(II) sulfateundergoes electrolysis using carbon(inert) electrodes.

Reaction at the anode: oxygen isproduced

Reaction at the cathode: copper metalis deposited on the cathode.

4 Active electrodes The following reactions occur at the

electrodes when copper(II) sulfateundergoes electrolysis using copper(active) electrodes.

Reaction at the anode: copper goesinto solution as copper ions, and theanode grows smaller.

Reaction at the cathode: copper metalis deposited, and the cathode growsbigger.

122

anodecathodeelectrodeelectrolysisinert

Key words

+ – + –

+ – + –

+ – + –

1 Dilute solutionsodium chloride

2 Concentrated solutionsodium chloride

3 Inert electrodes

4 Active electrodes

carbonelectrodes

dilute sodiumchloride solution

concentrated sodiumchloride solution

carbonelectrodes

carbonelectrodes

copper (II) sulfatesolution


carbonelectrodes

copperelectrodes



copperelectrodes

copperdeposited

Electrolysis: electrodeactivity and concentration

CHEMICAL REACTIONS

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Acids: reactions

1 Main reactions of an acid Dilute acids react with all metal

carbonates to give a metal salt, carbondioxide, and water.

Dilute acids react with bases to givesalts plus water.

Dilute acids react with most metals togive a metal salt and hydrogen.

Dilute acids are neutralized by metaloxides and metal hydroxides to form ametal salt and water.

2 Example of reaction type Sodium carbonate reacts with dilute

nitric acid to give sodium nitrate,carbon dioxide, and water.

Hydrochloric acid reacts with sodiumhydroxide to form a salt and water.

Zinc reacts with dilute hydrochloricacid to give zinc chloride andhydrogen.

Copper(II) oxide reacts with dilutesulfuric acid to give copper(II) sulfateand water.

3 Sulfur trioxide Sulfur trioxide is a white crystalline

solid obtained by oxidation of sulfurdioxide. It dissolves in water with ahissing noise and the production ofheat, forming sulfuric acid. Sulfurtrioxide is employed as a dehydratingagent.

Sulfur trioxide is made in thelaboratory by passing a mixture of drysulfur dioxide and dry oxygen over aheated platinum catalyst. Sulfurtrioxide melts at 17°C and condensesas a solid in a suitably cooled beaker.

Industrially it is made using thecontact process (see pages 75 & 76).

acidbasecarbonatecatalysthydroxide

oxidationoxidesalt

Key words

Acid with carbonate

Acid with base

Acid with metal

Acid neutralizedby oxide

Na2CO3(s) + 2HNO3(aq) 2NaNO3(aq) + CO2(g) + H2O(l)

HCl(aq) + NaOH(s) NaCl(s) + H2O(l)

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

CuO(s) + H2SO4(aq) CuSO4(aq) + H2O(l)

1 Main reactions of an acid

3 Laboratory preparation of sulfur trioxide

a oxygenb dry SO2c plantinized asbestos as a catalystd combustion tubee crushed ice and saltf white smoke of SO3g heat

a

b

c d

g

e

f

acidsalt +CO2+ H2O

salt+ H2O

salt+ H2

carbonate

metalbase

2 Examples of reaction type

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Preparation of acidsCHEMICAL REACTIONS

1 Preparing HCl gas Hydrogen chloride gas is made by the

reaction of sodium chloride andconcentrated sulfuric acid:2NaCl(s) + H2SO4(aq)

Na2SO4(aq) + 2HCl(g)

The gas is more dense than air and iscollected by downward delivery.

2 Preparing HCl acid Hydrogen chloride is extremely

soluble in water, forming hydrochloricacid. It cannot be dissolved simply byplacing a delivery tube carrying the gasdirectly into water because the waterwould be sucked back into thereaction vessel.

The gas is dissolved in water bypassing it into an inverted funnelpositioned so the lip is just under thesurface of the water. The funnelprevents suck back.

3 Preparing nitric acid Nitric acid can be made by the

reaction of solid sodium or potassiumnitrate with concentrated sulfuric acid:KNO3(s) + H2SO4(aq)

KHSO4(aq) + HNO3

The product of this reaction isnormally yellow due to the presenceof nitrogen dioxide, formed by thethermal decomposition of the acid:4HNO3(l)

4NO2(g) + 2H2O(g) + O2(g)

4 Industrial preparation of HNO3 Nitric acid is made industrially by the

oxidation of ammonia in a processinvolving three stages (see page 76):production of nitrogen oxide gas,oxidation of nitrogen oxide to nitrogendioxide gas, reaction of nitrogendioxide and water.

This process can be modeled in thelaboratory by passing ammonia vaporover a heated platinum catalyst.

124

hydrochloric acidhydrogen

chloridenitric acidsoluble

sulfuric acid

Key words1 Preparation of hydrogenchloride (gas)

3 Laboratory preparation of nitric acid

2 Preparation ofhydrochloric acid

a

bc

dg

h

j

k

l

m n

o

p

q

e

f

i

4 Industrial preparation of nitric acid

a rock saltb concentrated sulfuric acidc HCl gas collectedd heat

l concentratedammonia dilutedwith water (50%)

m combustion tuben platinized asbestoso pump sucks gases

through apparatusp brown gasq litmus goes red

h

e HCl filterf filter funnelg water (to become dilute

HCl acid)

h heati solid sodium nitrate

plus concentratedsulfuric acid

j water jacketk pure nitric acid

CHEMICAL REACTIONS

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Bases: reactions

Bases A base is a compound that reacts with

an acid to form a salt. Common basesare metal oxides, metal hydroxides,and metal carbonates.

1 General reactions withacids Metal oxides react with acids to form

salts and water. Metal hydroxides also react with acids

to form salts and water. Metal carbonates react with acids to

form salts, water, and carbon dioxide.

2 Metal oxide and acid The reaction of magnesium oxide

(MgO) with hydrochloric acid (HCl)can be followed by adding a few dropsof universal indicator to the acid.

Initially the indicator is red. Whenmagnesium oxide is added to thereaction, the following reaction occurs:MgO(s) + 2HCl(aq)

MgCl2(aq) + H2O(l)

When there are equivalent amounts ofmagnesium oxide and hydrochloricacid, the indicator turns green,signifying all of the acid has reactedand the mixture is neutral.

3 Carbonate and acid The reaction of magnesium carbonate

(MgCO3) with hydrochloric acid (HCl)can be followed by observing thecarbon dioxide gas evolved.

Initially bubbles of gas are evolved asthe following reaction occurs:MgCO3(s) + 2HCl(aq)

MgCl2(aq) + H2O(l) + CO2(g)

When all of the hydrochloric acid hasreacted, no gas is produced, andexcess insoluble magnesium carbonateremains in the beaker.

acidbasecarbonatehydroxideoxide

saltuniversal

indicator

Key words1 General reactions of a base with an acid

acid metaloxide

salt water

CO2acid metalcarbonate

salt water

acid metalhydroxide

salt water

+

+

+

+

+

+ +

2 Metal oxide and acid

heat is applied

Cabonate is added to hydrochloricacid and indicator

Neutral solution, indicator is greenMagnesium oxide is added to hydrochloricacid and indicator

3 Carbonate and acid

Neutral solution, indicator is green

gasbubble

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Bases: forming pure saltsCHEMICAL REACTIONS

1 From a soluble base Titration is used to make salts from

acids and soluble bases, e.g., sodiumchloride from hydrochloric acid andsodium hydroxide.

The burette is filled with hydrochloricacid, and a known volume of sodiumhydroxide solution is placed in aconical flask. A few drops of a suitableindicator are added to the sodiumhydroxide solution. Hydrochloric acidis run into the flask until the color ofthe indicator changes, showing thatthe reaction mixture is neutral. Thevolume of hydrochloric acid in theburette is noted before and afteraddition so the volume of acid neededcan be calculated.

The flask contains a solution ofsodium chloride, which is impure dueto the presence of the indicator. Theprocedure must be repeated usingexactly the same volumes ofhydrochloric acid and sodiumhydroxide solution but no indicator.

Sodium chloride crystals are obtainedby boiling off some of the water fromthe sodium chloride solution andallowing the remaining solution tocool.

2 From an insoluble base Salts are made from insoluble bases by

adding an excess of the base to anacid. For example, copper(II) sulfate isformed by the reaction of copper(II)oxide and sulfuric acid.

An excess of copper(II) oxide is usedto ensure that all of the sulfuric acidhas reacted and no acid residueremains. The excess is filtered off,leaving a blue solution of copper(II)sulfate.

Copper(II) sulfate crystals are obtainedby boiling off some of the water fromthe copper(II) sulfate solution andallowing the remaining solution tocool.

126

acidbaseindicatorinsolubleneutral

saltsolubletitration

Key words

Filter off excesssolid and collectthe filtrate

1 From a soluble base (alkali)Example: sodium chloride from sodium hydroxide and hydrochloric acid

Evaporate off filtrate

a buretteb acidc alkali and phenolphthalein indicator

Add the acid until the solution just turnscolorless.

d volume of acid in the burette before carryingout the procedure

e volume of acid remaining when the indicatorhas turned colorless

f salt solutiong boiling waterh heati neutralized acidj excess solid

2 From an insoluble baseExample: copper oxide and sulfuric acid

Warm gently, addingthe base until nomore will dissolve

Add the base todilute acid

a

b

c

d

g

h

j

e

f

i

h

h

0

5

10

15

20

25

0

5

10

15

20

25

Repeat the procedure,but without using theindicator, adding theamount of acidmeasured above(i.e., e–d)

Evaporate offexcess water

Measure the volumeof acid needed forneutralization (e–d)

Set up theapparatusas shown

h

CHEMICAL REACTIONS

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Proton transfer:neutralization of alkalis

1 Water particles In a water molecule, the oxygen atom

forms bonds with two hydrogenatoms. The oxygen atom and thehydrogen atom each donate oneelectron to the bond. The oxygenatom also has two pairs of non-bonding electrons, which can bedonated to form bonds with otherspecies.

In acidic solutions, each proton reactswith a water molecule to form ahydronium ion. A pair of non-bondingelectrons forms the new H-O bond:H+ + H2O H3O+

An hydroxide ion is formed by the lossof a proton from a water molecule:H2O H+ + OH-

2 Ammonium ions The ammonia molecule, NH3, has a

similar structure to the watermolecule, H2O, in the sense that thenitrogen atom has a pair of non-bonding electrons that it can donate toform a bond with another species.

Ammonia reacts with the protons in anacid to form the ammonium ions:NH3 + H+ NH4

+

The four N-H bonds in the ammoniumion are directed toward the corners ofa tetrahedron, giving a similarstructure to methane. This keeps thebonding pairs of electrons as far awayfrom each other as possible.

3 Schematic of protontransfer Ammonia is very soluble in water and

dissolves to form a weak alkalinesolution that is sometimes referred toas ammonium hydroxide:NH3 + H2O NH4OH NH4

+ + OH-

Ammonia solution containsammonium ions, NH4

+, and hydroxideions, OH-, and has similar reactions tosolutions of soluble metal hydroxides,such as sodium hydroxide.

ammoniumhydroxide

ammonium ionhydronium ionhydroxide ion

protonspecies

Key words

O

H

H

N

O

HH

HOH

H

N

H

O

H

H

H

N

H

H H

H

OH

H

H

H

OH

H

H

H

H

NH O

H

1 Water particles

molecules

Hydronium ion:protonated watermolecule

Neutral water molecule Hydroxide ion:deprotonated watermolecule

2 Ammonia solution turns universal indicator blue

To show the attraction between themolecules and the breaking of thebond in the molecule

Ammonia molecule hasan extra proton

To show the extra-electron in thehydroxide ion

ions

3 Schematic of proton transfer in diagram 2

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Proton transfer:neutralization of bases

CHEMICAL REACTIONS

Neutralizing bases Metallic bases neutralize acids to form

a salt plus water.

1 MgO in acid Magnesium oxide consists of a regular

lattice of magnesium ions, Mg2+, andoxide ions, O2-.

An acid contains hydronium ions,H3O+.

2 Attractions Hydronium ions carry a positive

charge, while oxide ions carry anegative charge. When solidmagnesium oxide is added to an acid,these oppositely charged ions areattracted to each other.

3 Transfer In an oxide ion, there are eight

electrons in the outer orbital of theoxygen atom. Two pairs of electronsare donated to form bonds withoppositely charged hydronium ions:2H3O+ + O2- 3H2O

4 Neutral solution Each hydronium ion transfers a proton

to the oxide ion, forming a moleculeof water.

The magnesium oxide lattice breaksdown, releasing magnesium ions intosolution.

The acid is neutralized, and a solutionof a magnesium salt is formed. Thenature of the salt depends on the acidused.MgO(s) + 2HCl(aq)

MgCl2(aq) + H2O(l)

Hydrochloric acid magnesium chloride

MgO(s) + 2HNO3(aq)

Mg(NO3)2(aq) + H2O(l)

Nitric acid magnesium nitrate

MgO(s) + H2SO4(aq)

MgSO4(aq) + H2O(l)

Sulfuric acid magnesium sulfate

128

acidbasehydronium ionlattice

magnesium oxideoxideprotonsalt

Key words

1 Magnesium oxide (MgO)solid and dilute acid

2 The oxide ions attract thehydronium ions

3 Proton transfer takesplace

4 A neutral solution isproduced and part of theoxide lattice has dissolved

H

H H

O

+

H

HH

O

+

Mg2+ O2– O2–Mg2+ Mg2+ O2–O2–Mg2+

Mg2+O2–

O2–Mg2+

Mg2+ O2–

H

H HO+

H

H

H

O +

H

H HO+

H

H

H

O+

Mg2+

H

HOH

H

O

HH

O

watermolecule

hydroniumion

magnesiumoxide lattice

CHEMICAL REACTIONS

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Proton transfer: metallic carbonates

Metallic carbonates Metallic carbonates neutralize acids to

form a metal salt, carbon dioxide, andwater.

1 Attraction Group 1 metal carbonates are soluble

in water and can be used as solids orin solution. Other metal carbonatesare insoluble in water and are used assolids.

All metal carbonates contain thecarbonate ion, CO3

2-. All acids containthe hydronium ion, H3O+.

Hydronium ions carry a positivecharge, while carbonate ions carry anegative charge. When a carbonate isadded to an acid, these oppositelycharged ions are attracted to eachother.

In a carbonate ion, each of the threeoxygen atoms has eight electrons in itsouter orbital. A pair of electrons isdonated from two of the oxygen atomsto form bonds with oppositely chargedhydronium ions.

2 H2CO3 and water The result is the formation of

carbonic acid, H2CO3, and water:2H3O+ + CO3

2- H2CO3 + 2H2O

3 H2CO3 splits Carbonic acid is a weak acid that only

exists in solution. It readily breaksdown to carbon dioxide and water:H2CO3 H2O + CO2

4 CO2 and water In an acid–carbonate reaction, some of

the carbon dioxide will remain insolution, but most will be given off asbubbles of gas.

The gas can be identified by bubblingit into limewater. Carbon dioxide turnslimewater milky due to the formationof insoluble calcium carbonate.

The acid is neutralized by thecarbonate, and a salt is formed. Thenature of the salt depends on themetal carbonate and the acid used.

carbonatecarbonic acidhydronium ion

orbitalsalt

Key words

O

O

H

H

OH H

H

OH

H H

O

H H

O

H H

O

HH

C

OCO

H

H

O

O

C

O– O–

O

CO O

1 Carbonate ions attracthydronium ions

carbonateion (CO2–

3 )

2 Hydrogen carbonatemolecules and watermolecules are produced

3 A hydrogen carbonatemolecule splits

4 A carbon dioxide moleculeand water molecule areproduced

protontransfer

watermolecule

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Proton transfer:neutralization of acids

CHEMICAL REACTIONS

Neutralizing acids Bases react with acids to produce a

salt and water.

1 Molecules A chlorine atom has seven electrons in

its outer orbit. In hydrogen chloride,the chlorine atom forms a covalentbond with one hydrogen atom,forming the molecule HCl.

An oxygen atom has six electrons in itsouter orbit. In hydrogen oxide (water),the oxygen atom forms covalent bondswith two hydrogen atoms, forming themolecule H2O.

A nitrogen atom has five electrons inits outer orbit. In ammonia, thenitrogen atom forms covalent bondswith three hydrogen atoms, formingthe molecule NH3.

2 Schematic In a hydrogen chloride molecule, each

chlorine atom is surrounded by eightelectrons: one pair of bondingelectrons and three pairs of non-bonding electrons (lone pairs).

In a water molecule, each oxygen atomis surrounded by eight electrons: twopairs of bonding electrons and twolone pairs of electrons.

In an ammonia molecule, eachnitrogen atom is surrounded by eightelectrons: three pairs of bondingelectrons and one pair lone pair ofelectrons.

3 & 4 Proton transfer andschematic Hydrogen chloride gas is a covalent

compound and exists as diatomicmolecules.

When hydrogen chloride dissolves inwater, an acidic solution is formed:H2O + HCl H3O+ + Cl-

A lone pair of electrons from anoxygen atom is donated to create acovalent bond between the oxygenatom and a hydrogen atom, forming ahydronium ion and a chloride ion.

When hydrogen chloride is dissolvedin water, it forms an ionic compound.

130

ammoniacovalent bond

hydrogenchloride

Key words

O

H

H

O

HH

Cl

Cl

H

O

H H

H

N

H

O

H

Cl

H H

N

HH

H

O

H H

H

Cl

H

H

OH

Cl

H

HH Cl O

H

H

HCl

1 Examples of molecules

3 Proton transfer

4 Schematic of proton transfer

2 Schematic of the molecules shown in diagram 1

Hydrogen chloridemolecule

lonepairs

lonepairs

lone pairsWater molecule

lone pairsAmmonia molecule

Hydrogen chloridemolecule

Water molecule Ammonia molecule

lone pairslone pairs

A water molecule withone extra proton

A chlorine atom withone extra proton

Attraction begins The bond breaks Transfer of the protonis complete

CHEMICAL REACTIONS

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Collision theory

1 Collision theory Reactions occur when particles collide

with sufficient force to provide theenergy needed to start a reaction.

If particles collide with insufficientforce to start a reaction, they simplybounce off each other.

A collision that brings about a reactionis called an effective collision. Particlesof reactant collide, and particles ofproduct are formed:

A + B C + D

reactants products Not every collision between particles

gives rise to a reaction, but every set ofparticles that do react have to collide.

2 Maxwell-Boltzmandistribution Because all the particles of a particular

chemical, element, or compound havethe same mass, the energy of theparticles is directly related to theirspeed.

In any mixture of moving particles, theenergy at which an individual particleis moving will vary.

The Maxwell-Boltzman distributionshows how the number of particles ina sample is distributed at differentenergies at a particular temperature.

There are no particles at zero energy.There are relatively few particles atvery high energy, but there is nomaximum energy value.

In order to react, particles need tohave a minimum amount of energy,called activation energy. Theactivation energy is marked on thegraph by a line, parallel to the Y axis,at a point on the X axis thatsymbolizes the activation energy (EA).

activation energy effective collisionproductreactant

Key words

No collision between the particles of the reactants: no reaction

Weak collision: no reaction

Effective collision: reaction

1 Collision theory

A A

BB

A BAB

A DCB

2 Maxwell-Boltzman distribution

Kinetic energy

Num

ber

ofpa

rtic

les

wit

hen

ergy

(E)

EA

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Rates of reaction:surface area and mixing

CHEMICAL REACTIONS

Surface area In order for a reaction to take place,

the reactants must come into contactwith each other. Thus, for a given massof reactant, the smaller the objects, thegreater the surface area on which thechemical reaction can occur. If all ofthe reactants are gases or liquids, it iseasy for them to mix, giving themaximum opportunity for the particlesto collide.

1 Total surface area The reaction can only take place on

the surface of the solid. A cube with sides 2 cm has a total

surface area of 2 x 2 x 6 = 24 cm2. Ifthe same cube is divided into 8 cubeswith sides 1 cm, the total surface areanow becomes 1 x 1 x 6 x 8 = 48 cm2.

2 Reduced surface area Zinc reacts with dilute hydrochloric

acid to form zinc chloride andhydrogen gas:Zn + 2HCl ZnCl2 + H2

This reaction proceeds much morequickly if zinc dust (fine powder) isused rather than granulated zinc (largelumps).

3 Mixing When reactant particles are added

together, they will eventually mix bydiffusion, and a reaction will takeplace.

Stirring reactants speeds the processof mixing so the reaction takes placemore quickly.

4 Interface surface area If one of the reactants is a liquid and

one a gas, or if the two reactants areimmiscible liquids, then the reactioncan only take place at the interface.The larger the surface area of theinterface, the faster the reaction willtake place.

132

diffusionimmisciblereactantsurface area

Key words

1 Total suface area

largeinterface

smallinterface

1 cm1 cm

1 cm2 cm

2 cm

2 cm

2 Reduced surface area reaction

3 Mixing

4 Interface surface area

zinc dustgranulated

zinc

B

A A AA

A A A

B B

B

B

B B

B

A

A

A

A

A

A

A

B

B

B

B

B

B

diffusion

slow

stirring

rapid

CHEMICAL REACTIONS

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1 Temperature Temperature is an important factor in

determining rate of reaction. When temperature increases, the

average speed of the particles in asubstance increases. The graph shows the Maxwell-Boltzmandistribution at two temperatures, T2

is greater than T1. The number of particles is constant, so

the area under the two curves is thesame. However, the average energy ofthe particles at T2 is greater. The areaof the curve to the right of theactivation energy line (EA) is greaterfor T2. Therefore, at this temperature ahigher proportion of particles havesufficient energy to react.

2 Concentration An increase in the concentration of a

chemical, or the pressure of a gas,means that there will be more particleswithin a given space, so particles willcollide more often.

3 Rate of reaction The rate of any reaction is the speed at

which the reactants are converted toproducts. This can be qualified as thechange of concentration of reactantsor products.

Changes in concentration can bemeasured by:1. appearance or disappearance ofcolor in reactants or products2. volume of gas evolved3. changes in pH4. heat produced5. changes in pressure.

activation energyproductreactant

Key words

B

A

A

A

A

A

A

A

B

B

B

B

B

B

Rate of reaction =Change in concentration

Time

3 Rate of reaction

Low concentration High concentration

A

A

B

A

BAA

B

BA

A

AB

B

B

A

A

B B

A

B A

A

A

B

B B

A

2 Concentration

1 Temperature (distribution of molecularenergies at T1 and T2)

Kinetic energy

Num

ber

ofpa

rtic

les

havi

nga

give

nen

ergy

EA

T1

T2

Rates of reaction:temperature andconcentration

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Rates of reaction:concentration over time

CHEMICAL REACTIONS

Concentration over time Bromine reacts with an excess of

methanoic acid in aqueous solutionaccording to the following equation.The reaction is catalyzed by acid:

H+

Br2(aq) + HCOOH(aq)

2Br-(aq) + 2H+(aq) + CO2(g)

The reaction can be followed bymeasuring the intensity of the red-brown at different time intervals andrelating this to the concentration ofbromine.

The concentration of bromine, [Br2],falls during the reaction, so the rate ofthe reaction can be expressed in termsof the rate at which the bromineconcentration changes.

The rate of reaction =- rate of change of bromineconcentration = - d[Br2]

dt

The rate of change of bromineconcentration is negative because thebromine is being used up. Thenegative sign in the expression isnecessary to give the rate of reaction apositive value.

In order to obtain the rate of reactionat any given time, a tangent to thecurve must be drawn at that particulartime and the gradient measured. Theconcentration of bromine after 300seconds (s) is 0.0035 mol dm-3. Therate of reaction at this time is 1.2 x 10-5

mol dm-3 s-1.

134

concentrationrate of reaction

Key words

[Br 2

]m

ole

dm–3

0.004

Time (seconds)

100

Tangent attime = 300s

700200 300 400 500 6000

0.010

Graph to show the variation of bromine concentration with time in the reactionbetween methanoic acid and bromine

0.009

0.008

0.007

0.006

0.005

0.003

0.002

0.001

0

CHEMICAL REACTIONS

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Rate of reaction vs.concentration

Rate vs. concentration In order to draw a graph showing how

the rate of reaction varies withbromine concentration, it is necessaryto find the rate of reaction at differenttimes and, therefore, differentbromine concentrations.

The graph shows that the rate ofreaction is directly proportional to thebromine concentration. Reaction rate [Br2], therefore,Rate of reaction = k[Br2] where k is aconstant, known as the rate constantor the velocity constant for thereaction.

This reaction is said to be first ratewith respect to bromine sincedoubling the concentration of brominedoubles the rate of the reaction.

Since rate of reaction = k[Br2], then tofind the units of k:k = rate of reaction =

[Br2]

mol dm-3 s-1 = s-1

mol dm-3

The unit of the rate constant, k, forfirst order reactions is s-1.

concentrationrate of reaction

Key words

/m

ole

dm–3

s–1

1.2

0.001 0.0070.002 0.003 0.004 0.005 0.0060

3.0

Graph to show the variation of reaction rate with bromine concentration

2.7

2.4

2.1

1.8

1.5

0.9

0.6

0.3

0

[Br2] / mole dm–3

0.008

–d[B

r 2]

×10

5

dt

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Variation of reaction rateCHEMICAL REACTIONS

1 Clock technique Rate of reaction =

change in concentration of a substancetime

In order to monitor the progress of areaction, we could measure theconcentration of a reactant or aproduct at regular time intervals, sayevery 10 seconds.

Strictly speaking, this would give usthe average reaction rate during the 10second period. By measuring thechange in concentration over shorterand shorter time periods, we wouldobtain an increasingly more accurateestimate of the rate of reaction at anyparticular moment.

Using a clock technique, the rate isobtained as the inverse of the time fora certain proportion of the reaction tooccur. Provided the reaction has onlygone a small way toward completion,the error is very small, but the errorincreases as the reaction movesfurther to completion.

2 Increasing concentration If doubling the concentration of a

reactant has no effect on the rate of areaction, then the reaction is said tobe zero order with respect to thereactant. The rate equation is:rate = k[reactant]0 = k

If doubling the concentration of areactant doubles the rate of a reaction,then the reaction is said to be firstorder with respect to the reactant. Therate equation is:rate = k[reactant]

If doubling the concentration of areactant quadruples the rate of areaction, then the reaction is said tobe second order with respect to thereactant. The rate equation is:rate = k[reactant]2

136

concentrationproductrate of reactionreactant

Key words

Time/s

Concentration of X

true initial rate

average reaction rate for 10% completion

average reaction rate for 50% completion

zero order

first order

second order

1 Clock technique for measuring reaction rates

2 Increasing concentrationThe variation of reaction rate with concentration for reactions whichare zero, first, and second order

%of

reac

tion

com

plet

ed

100

90

80

70

60

50

40

30

20

10

0

321

3

2

1

Rea

ctio

nra

te

1

23

1

2

3

CHEMICAL REACTIONS

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Rates of reaction: effectof temperature 1

Effect of temperature When a substance is heated, its

particles gain kinetic energy and movearound more quickly. The frequency ofcollisions increases, and because theparticles have a greater momentum,the frequency of effective collisionsalso increases. The result is an increasein the rate of reaction.

1 Most reactions In most chemical reactions, the rate of

reaction increases steadily with risingtemperature. It is for this reason thatchemical reactions are often heated.

2 Enzyme-catalyzedreactions Enzymes catalyze chemical reactions

with a high degree of specificity andefficiency. An enzyme molecule is apolymer composed of a long chain ofamino acids that folds over on itself,giving it a particular shape. Reactingmolecules, called the substrate, fit intothis shape rather like a key in a lock.

Up to a point, the rate of an enzyme-catalyzed reaction increases with risingtemperature in the same way as mostother reactions. However, afterreaching an optimum temperature atwhich the activity of the enzyme isgreatest, the reaction rate rapidly falls.

Heating an enzyme causes its shape tochange, and thus the enzyme ceases tobe able to catalyze the reaction. It issaid to be denatured.

3 Explosive reactions In an explosive reaction, the reaction

rate increases with rising temperatureup to some point where the reactionrate suddenly rises sharply.

effective collisionenzymekinetic energypolymerrate of reaction

Key words

Temperature

Rea

ctio

nra

te

Temperature

Rea

ctio

nra

te

Temperature

Rea

ctio

nra

te

The effect of temperature on different reactions

1 Most reactions

2 Enzyme-catalyzed reactions

3 Explosive reactions

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Rates of reaction: effectof temperature 2

CHEMICAL REACTIONS

1 Rate constant forreaction As a general rule of thumb, the rate of

a reaction doubles for every 10 K risein temperature. This would seem tosuggest that there is an exponentialrelationship between rate andtemperature.

The exact relationship was proposedby the Swedish chemist SvanteArrhenius in 1889. The Arrheniusequation relates the rate constant (notthe rate of reaction) to temperature.

The equation can be expressed in alogarithmic form and in terms of log tothe base 10. The latter form of theequation is the most useful forcalculation purposes.

2 Plotting the Arrheniusconstant The constants A and Ea for a given

reaction can be obtained by plottinglog k against 1/T: the temperature, T,must be expressed in kelvin. The slope of the graph is equal to Ea / 2.303R.

The Arrhenius constant, A, can beobtained by substituting values for theslope (Ea / 2.303R), log k and T in theArrhenius equation.

The activation energy, Ea, can also befound from the slope of the graph.Slope = - Ea / 2.303 R

The slope of the graph is negative, andits unit is K thereforeEa = 2.303 x R x slopeThe gas constant, R, = 0.008314 kJ

K-1 mol-1 thereforeEa = 2.303 x 0.008314 x

slope kJ mol-1

138

activation energy

Key words

y

x

yxslope =

k = Ae–Ea/RT

In k = ln A – Ea/RT

log k = log A – Ea/2.303RT

k = rate constant for the reaction

A = constant for the reaction (Arrhenius constant)

Ea = activation energy

R = gas constant

T = absolute temperature

1 Rate constant for reaction

2 Plotting the Arrhenius constant

Log

(k/s

–1)

T–1/k–1

CHEMICAL REACTIONS

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Exothermic andendothermic reactions

1 Exothermic In an exothermic reaction, energy is

given out, and the temperature of thereaction mixture increases as thereaction proceeds. The products are ata lower energy than the reactants.

The energy released is due to adecrease in the enthalpy, DH, of thesystem. Enthalpy is a measure of thestored heat energy of a substance.Therefore, DH is negative for anexothermic reaction.

The following equation represents thecombustion of methane in a goodsupply of air:CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

DH= -890 kJ mol-1

This is an exothermic reaction. 890 kJof energy are released per mole ofmethane combusted.

2 Endothermic In an endothermic reaction, energy is

taken in, and the temperature of thereaction mixture decreases as thereaction proceeds. The products are ata higher energy than the reactants.

The energy taken in is due to anincrease in the enthalpy, DH, of thesystem. Therefore, DH is positive foran endothermic reaction.

The following equation represents thesteam reforming of methane:CH4(g) + H2O(g) 3H2(g) + CO(g)

DH = +206 kJ mol-1

This reaction is an endothermicreaction. 206 kJ of energy are taken inper mole of methane reformed.

endothermicenthalpyexothermicproductreactant

Key words

EA

∆H

EA

∆H

EA = activation energy ∆H = heat of reaction

1 Exothermic

2 Endothermic

Ene

rgy

reactants

products

Ene

rgy

reactants

products

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Average bonddissociation energies

CHEMICAL REACTIONS

1 Average bond enthalpy Bond dissociation energy is the

energy change when one mole ofbonds is broken. It refers to a specificbond in a molecule. However, theexact value depends on the localenvironment of the bond. Forexample, if the C-H bonds in methaneare broken one after another, each willhave a different bond dissociationenthalpy:CH4(g) CH3(g) + H(g)

DH = +425 kJ mol-1

CH3(g) CH2(g) + H(g)

DH = +470 kJ mol-1

CH2(g) CH(g) + H(g)

DH = +416 kJ mol-1

CH(g) C(g) + H(g)

DH = +335 kJ mol-1

For this reason, in a moleculecomposed of more than one atom, it ismore useful to know the averageamount of energy needed to break aparticular bond.

2 Estimating enthalpychange The table at right utilizes the complete

combustion of propane to illustratehow bond enthalpies can be used toestimate the enthalpy change in areaction.

6,488 kJ mol-1 of total energy is takenin to break the bonds.

8,542 kJ mol-1 of total energy is givenout when the bonds are formed.

The enthalpy change when 1 mole ofpropane is completely combusted is6,488 – 8,542 = 2,054 kJ mol-1.

140

dissociationenthalpy

Key words

The enthalpy change when 1 mole of propane is completely combusted is

6,488 – 8,542 = 2,054 kJ mol–1.

1 Average bond enthalpy

Bond Average bondenthalpy / kJ

mol–1

347

612

346

413

286

336

C=O

H–Cl

H–H

N–H

O–H

805

432

436

391

464

498

C–C

C=C

C–Cl

C–H

C–N

C–O

Bond Average bondenthalpy / kJ

mol–1

O=O

2 Estimating the enthalpy change in a reaction.Complete combustion of propane.

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

Energy is taken in to break bonds:

Bond

C–HC–CO=O

Total energy taken in

Average bonddissociationenergy / kJ mol–1

413347498

Numberof bonds

825

Energy takenin / kJ mol–1

3,304694

2,490

6,488

Bond

C=OO–H

Total energy taken in

Average bonddissociationenergy / kJ mol–1

805464

Numberof bonds

68

Energy takenin / kJ mol–1

4,8303,712

8,542

Energy is given out when bonds are formed:

CHEMICAL REACTIONS

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Catalysts: characteristics

Catalysts A catalyst is a substance that alters the

rate of a chemical reaction but remainschemically unchanged by it.

1 Characteristics ofcatalysts Catalysts may be classified as

homogenous or heterogeneous.Homogenous catalysts are in the samephase (solid, liquid, or gas) as thereactants; heterogeneous catalysts arein a different phase.

A large number of reactions arecatalyzed on the surface of solidcatalysts. The surface provides activesites where reactions can occur. Thus,an increase in the surface area willincrease the effect of the catalyst.

2 Increasing reaction rate Hydrogen peroxide decomposes very

slowly on its own to form water andoxygen gas:2H2O2(aq) 2H2O(l) + O2(g)

The rate of this reaction is greatlyincreased by adding manganesedioxide, MnO2.

Manganese dioxide acts as a catalystand remains unchanged after all of thehydrogen peroxide has decomposed.

3 Activation energies A catalyst lowers the minimum energy,

or activation energy (EA), required fora reaction to occur. The frequency ofeffective collisions is, therefore,increased, resulting in an increase inthe rate of a reaction.

activation energyactive sitecatalysteffective collision

Key words

2 Increasing reaction rate

1 Characteristics of catalysts

Manganese dioxideremains at the end

of the reaction

Specificity

Stoichiometry

Reaction mechanism

Chemical involvement

Equilibrium

Yield

The overall stoichiometry of a reaction is unaltered.

Catalysts may alter the rate of one reaction but have no effecton others.

A catalyst provides an alternative reaction pathway for areaction to take place.

A catalyst is chemically involved in a reaction. It is consumedduring one step and regenerated in another. A catalyst doesnot undergo a net chemical change, but it may change itsphysical form.

A catalyst speeds up the rates of both forward and backwardreactions, and this speeds up the rate at which equilibriumis attained.

A catalyst does not alter the yield of a reaction.

Manganesedioxidecatalyst

3 Distribution of the kinectic energies of reacting particlesand the activation energies for catalyzed and uncatalyzedreactions

Kinetic energy (E)

Num

ber

ofpa

rtic

les

wit

hen

ergy

(E)

EAEA

EA for catalyzed reaction

EA for uncatalyzed reaction

Fraction of particles withE >EA for uncatalyzedreaction

Extra fraction of particles with E >EAfor catalyzed reaction

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Catalysts: transitionmetals

CHEMICAL REACTIONS

1 Reaction catalyzed Catalysts are often transition metals

or transition metal compounds.Transitional metals are useful ascatalysts because or their ability toexist in different oxidation states.

2 V205 as catalyst The contact process is an important

step in the manufacture of sulfuricacid (see pages 85 and 86). Sulfurdioxide is oxidized to sulfur trioxide inthe presence of a vanadiumpentoxide, V2O5, catalyst.

This reaction involves the reductionand subsequent oxidation of thecatalyst. In the reduction reaction, theoxidation state of vanadium changesfrom +5 to +4. In the oxidationreaction, it changes back from +4 to+5.

3 Iron as catalyst The Haber process for the

manufacture of ammonia uses finelydivided iron as the catalyst (see pages74 and 75):

Fe(s)

N2 + 3H2 2NH3

DH = -92 kJ mol-1

This reaction is exothermic. Accordingto Le Chatelier’s principle, a lowtemperature would produce moreammonia in the equilibrium mixture,but it would take longer to reachequilibrium.

The catalyst does not alter the yield ofammonia in the equilibrium mixture,but it does increase the speed withwhich equilibrium is attained. Using acatalyst, a reasonable rate of reaction isachieved at a lower temperature thanwould otherwise be the case.

142

catalystequilibriumexothermicLe Chatelier’s

principle

oxidationoxidation statereductiontransition metalsvanadium

Key words

1 Transition metals and reaction catalyzed

Transitionmetal/compound

Reaction catalyzed

polymerization of ethene to poly(ethene)

contact process in production of sulfuric acid

Haber process on production of ammonia

hydrogenation of alkenes in hardening of vegetable oils

oxidation of ethanol to ethanal

oxidation of ammonia in manufacture of nitric acid

TiCl3

V2O5

Fe

Ni

Cu

Pt

2 Vanadium oxide as catalyst in contact process

N2 + 3H2

2NH3

Ene

rgy

cont

ent

(kJ)

700

600

500

400

300

200

100

0

–100

–200

–300

uncatalyzed reaction

catalyzed reactionactivation energy foruncatalyzed reaction = 668kJ

activation energy forcatalyzed reaction = 212kJ

heat of reaction = –92kJ

V2O5(s)2SO2(g) + O2(g) 2SO3(g)

SO2 + V2O5 SO3 + V2O4

2V2O4 + O2 2V2O5

Fe(s)3 Iron as catalyst in Haber process

(Energy profiles for the reaction N2 + 3H2 2NH3)

CHEMICAL REACTIONS

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Oxidation and reduction

Evolving definition Over time, scientists have extended

the definitions of oxidation andreduction.

1 Oxygen Historically the terms oxidation and

reduction were applied to reactionsinvolving either the addition or theremoval of oxygen. For example:2Cu(s) + O2 2CuO(s)

copper is oxidizedFe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)

iron is reduced

2 Hydrogen The terms were extended to include

the removal or addition of hydrogen:CH3-CH3(g) CH2=CH2(g) + H2(g)

ethane is oxidizedCH3COH(l) + H2(g) CH3CH2OH(l)

ethanal is reduced

3 Modern definition The terms oxidation and reduction are

now used more widely to describechanges in oxidation state:Cu(s) Cu2+(aq) + 2e-

copper is oxidized to copper(II)Fe3+(aq) + e- Fe2+(aq)

iron(III) is reduced to iron(II) This definition covers all of those

reactions involving the gain or loss ofoxygen and other reactions that do notinvolve oxygen.

4 Redox reaction Reactions that involve a reduction

must also involve an oxidation. If onereactant is reduced, then another mustbe oxidized. Such reactions aredescribed as redox reactions.

oxidationoxidation stateredox reactionreduction

Key words

Oxidation is the addition of oxygen to a substance

Reduction is the removal of oxygen from a substance

Oxidation is the removal of hydrogen from a substance

Reduction is the addition of hydrogen to a substance

Oxidation is the loss of electrons from a substance

Reduction is the gain of electrons by a substance

1 Oxygen

Mg(s) + Cu2+ Mg2+(aq) + Cu(s)

oxidation

reduction

4 Redox reaction

2 Hydrogen

3 Modern definition

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Redox reactions 1CHEMICAL REACTIONS

Redox reactions Reduction and oxidation reactions

always occur together and arecollectively referred to as redoxreactions.

1 Oxidation and reduction When magnesium is heated in air, it

forms magnesium oxide:2Mg(s) + O2(g) 2MgO(s)

Magnesium atoms are oxidized tomagnesium ions by losing twoelectrons.

Oxygen atoms are reduced to oxideions by gaining two electrons.

This is true of all metals when they areconverted to metal oxides.

2 Electron transfer A more reactive metal displaces the

ions of a less reactive metal from asolution of its salts. This type ofreaction is called a displacementreaction:Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)

Zinc atoms are oxidized to zinc ions bylosing two electrons.

Copper ions are reduced to copperatoms by gaining two electrons.

3 Balancing redoxreactions In balancing redox reactions, the

electrons lost must equal the electronsgained.

In the example at right, bromine (a) isgaining two electrons and iron (b) islosing 1 electron.

In order to balance the equation, theentire reaction has to be multiplied by2 (c).

The result is a balanced equation (d).

144

displacementreaction

oxidationredox reactionreduction

Key words

2 Electron transfer in redox reactions

1 Redox reactions: oxidation and reduction

3 Balancing redox reactions

When powered zinc is added to copper sulfate (II) solution, an exothermic reaction occurs

The metal is oxidized and the metal is reduced. The oxygen takes the electrons givenup by the metal

When metals react with oxygen they form oxides

(c) Redox reaction

(d) Balance equation

(b) The reducing agent is Fe2+

(a) The oxidizing agent is Br2

Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

2Mg + O2 → 2Mg2+ + 2O2–

4Na + O2 → 2(Na2)2O2–

2Mg → 2Mg2+ + 4e–

O2 + 4e– → 2O2–

Zn(s) → Zn2+(aq) + 2e–

Cu2+(aq) + 2e– → Cu(s)Redox equations for the reaction

Br2 + 2e– → 2Br–

Fe2+ → Fe3+ + e–

2Fe2+ → 2Fe3+ + 2e–

Br2 + 2e– → 2Br–

2Fe2+ + Br2 → 2Fe3+ + 2Br–

CHEMICAL REACTIONS

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Redox reactions 2

1 Metals with non-metals Iron undergoes redox reactions with

non-metals.Iron and sulfur:Fe(s) + S(s) Fe2+S2-(s)

Iron atoms are oxidized to iron(II)ions by losing two electrons.Sulfur is reduced to sulfide ions bygaining two electrons.Iron and chlorine:2Fe(s) + 3Cl2(s) 2Fe3+Cl-3(s)

Iron atoms are oxidized to iron(III)ions by losing three electrons.Chlorine is reduced to chloride ions bygaining one electron.

2 Metals with water Metals are oxidized when they react

with water.Metal + water

metal hydroxide + hydrogen

Ca(s) + 2H2O(l)

Ca(OH)2(aq) + H2(g)

H2O(l) H+(aq) + OH-(aq)

Ca(s) + 2H+(aq) Ca2+(aq) + H2(g)

In the example at left, calcium atomsare oxidized to calcium ions by theloss of two electrons. Hydrogen ionsare reduced to hydrogen atoms bygaining one electron.

3 Metals with acids Metals are oxidized when they react

with acids.Metal + acid metal salt + hydrogen

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

Zn(s) + 2H+(aq) Zn2+(aq) + H2(g)

In the example at left, zinc atoms areoxidized to zinc ions by the loss of twoelectrons. Hydrogen ions are reducedto hydrogen atoms by gaining oneelectron.

redox reaction

Key words

2 The reaction of metals with water

1 The reaction of metals with non-metals

3 The reaction of metals with acids

Calcium and water

Iron and chlorine

Redox equation

Ca + 2H2O → Ca2+(OH–)2 + H2

Fe + S → Fe2+S2–

Fe → Fe2+ + 2e–

S + 2e– → S2–

2Fe + 3Cl2 → 2FeCl3

Ca → Ca2+ + 2e–

2H2O + 2e– → 2OH– + H2

Redox equation

Zn → Zn2+ + 2e–

2H+ + 2e– → H2

Iron and sulfur

Redox equation

Redox equation

The reaction of zinc

Zn(s) + 2H+(aq) → Zn2+(aq) + H2 →

2Fe → 2Fe3+ + 6e–

3Cl2 + 6e– → 6Cl–

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Demonstrating redoxreactions

CHEMICAL REACTIONS

1 Electron transfer in redoxreactions The movement of electrons during

redox reactions can be demonstratedusing a simple cell consisting of twometals rods, suspended in solutions oftheir salts, connected by a wire and asalt bridge.

At the zinc rod, zinc atoms lose twoelectrons to become zinc ions. Theelectrons pass along the wire andthrough the bulb to the copper rod.The zinc ions pass into solution.

At the copper rod, copper ions gaintwo electrons to become copperatoms. The copper ions come out ofsolution and are deposited as coppermetal on the copper rod.

Electric current passes through thewire in the external circuit as a flow ofnegatively charged electrons.

Ions flow through the salt bridge:positive ions from the zinc sulfatesolution to the copper sulfate, andnegative ions in the opposite directionfrom the copper sulfate solution to thezinc sulfate solution.

Electric current passes through ionicsolutions as a flow of positivelycharged and negatively charged ions.

2 Reaction equations Zinc is higher than copper in the

reactivity series. Zinc atoms areoxidized to zinc ions, while copperions are reduced to copper atoms.

When any two metals are placed in acell, the direction of electrons in theexternal circuit depends on theirreactivities. The metal that is higher inthe reactivity series will be oxidized,while the ions of the metal that islower in the reactivity series will bereduced.

146

reactivity seriesredox reaction

Key words

1 Electron transfer in redox reactions

a zinc rodb zinc sulfate solutionc electron flowd filter paper soaked in potassium

nitrate as a salt bridgee copper rod

f copper sulfate solutiong small light bulbh movement of negative charge (electrons

and anions)i movement of positive charge (cations)

2 Reaction equations

a

b

c d

e

f

i

g

h

Zn(s) + Cu2+ → Zn2+(aq) + Cu(s)

Zn(s) → Zn2+(aq) + 2e–

Cu2+(aq) + 2e– → Cu(s)

Copper ions are reduced to a deposit of red-brown

Experimental set-up

Movement of chargearound the circuit

2e–

Zn2+

NO–3

2e–

K+

CU2+SO4

2–

CHEMICAL REACTIONS

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Assigning oxidation state

1 Oxidation state The ability of transition metals to

exhibit different oxidation states indifferent compounds is central to thebehavior of these elements.

The oxidation state of simple ions isgiven by the charge they carry, e.g.:Na+ has an oxidation state of +1O2- has an oxidation state of -2

The situation is more complicated in acomplex ion. The oxidation state ofthe central atom in a complex ion isthe charge that the ion would have if itwere a simple ion. This is found byadding the oxidation states of thevarious components in the complexion.

2 Tetrachlorocuprate ion Total oxidation number due to

chlorine = 4 x -1 = -4. Overall charge on the ion = -2. Oxidation state of the central copper

atom = -2 – (-4) = +2. This complex ion is more correctly

called the tetrachlorocuprate(II) ion.

3 Manganate ion Total oxidation number due to oxygen

= 4 x -2 = -8. Overall charge on the ion = -1. Oxidation state of the central

manganese atom = -1 – (-8) = +7. This complex ion is more correctly

called the manganate(VII) ion.

4 Dichromate ion Total oxidation number due to oxygen

= 7 x -2 = -14. Overall charge on the ion = -2. Total oxidation state of the two central

chromium atoms = -2 – (-14) = +12. Oxidation state of each chromium

atom = +12 / 2 = +6. This complex ion is more correctly

called the dichromate(VI) ion.

oxidation statetransition metals

Key words

2

CuCl42–

the tetrachlorocuprate ion contains the transition metal copper

2 Tetrachlorocuprate ion

3

MnO4–

the manganate ion contains the transition metal manganese

3 Manganate ion

4

Cr2O72–

the dichromate ion contains the transition metal chromium

4 Dichromate ion

1 Oxidation state

Component Oxidation state

uncombined elements

Group 2 metals in compounds

Group 1 metals in compounds

combined hydrogen except in metal hydrides

combined hydrogen in metal hydrides

combined halogens

combined oxygen

0

+2

+1

+1

–1

–1

–2

The allotropes of carbon:diamond and graphite

CHEMISTRY OF CARBON

148

allotropecarbondiamondfullerenesgraphite

Key words

Carbon allotropes Carbon exists in three allotropes:

diamond, graphite, and fullerenes.

1 Diamond In diamond, each carbon atom is

covalently bonded to four othercarbon atoms.

The four bonds are directed towardthe corners of a pyramid ortetrahedron, and all bonds are thesame length, 0.154 nm. The anglebetween any two bonds is 109.5°.

All four of the outer electrons on thecarbon atom form bonds with othercarbon atoms so there are no mobileelectrons. Diamond does not,therefore, conduct electricity.

Diamond has a rigid structure and isvery hard.

2 Graphite The carbon atoms in graphite are

arranged in layers consisting ofinterlocking hexagons in which eachcarbon atom is covalently bonded tothree other carbon atoms. The lengthof the bond is 0.141 nm, and the anglebetween bonds is 120°.

The fourth outer electron on eachcarbon atom forms bonds withadjacent layers. The bond length ismuch greater than between carbonatoms within a layer.

The electrons between the layers aremobile; therefore, graphite conductselectricity. Also, the layers are able toslide over each other relatively easily.

Graphite is soft.

Bond angle 109.5°Bond length 0.154 nm

Bond angle 120°Bond lengths– in layers 0.141 nm– between layers 0.335 nm

Diamond

Graphite

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CHEMISTRY OF CARBON

149

allotropebuckyballcarbon

fullerenesgraphitenanotube

Key words

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Fullerenes Fullerenes are allotropes of carbon in

the form of a hollow sphere or tube.Spherical fullerenes are sometimescalled buckyballs, and cylindricalfullerenes are called nanotubes.

Because the allotrope was onlydiscovered in the late twentiethcentury, its physical and chemicalproperties are still being studied.

Fullerenes are not very reactive andare only slightly soluble in manysolvents. They are the only knownallotrope of carbon that can bedissolved.

Buckminsterfullerene This form of carbon is composed of 60

carbon atoms bonded together in apolyhedral structure composed ofpentagons and hexagons. Themolecules are made when an electricarc is struck between graphiteelectrodes in an inert atmosphere.This method also produces smallamounts of other fullerenes that haveless symmetrical molecular structures,such as C70.

Buckminsterfullerene was firstidentified in 1985 and named after thearchitect Richard Buckminster Fullerbecause of the resemblance of itsstructure to the geodesic dome.

The substance is a yellow crystallinesolid that is soluble in benzene, anorganic solvent.

It is possible to trap metal ions withinthe C60 sphere. Some of thesestructures are semiconductors.

Nanotubes Nanotubes, first identified in 1991, are

long thin cylinders of carbon closed ateither end with caps containingpentagonal rings.

Nanotubes have a very broad range ofelectronic, thermal, and structuralproperties that change depending onthe kind of nanotube (defined by itsdiameter, length, and twist).

Buckyball

Nanotube

The allotropes of carbon:fullerenes

The carbon cycleCHEMISTRY OF CARBON

150

atmospherecarboncarbon cyclechlorophyllglucose

photosynthesisrespiration

Key words

The carbon cycle Carbon is the fourth most abundant

element in the Universe. The total amount of carbon on planet

Earth is fixed. The same carbon atomshave been used in countless othermolecules since Earth began. Thecarbon cycle is the complex set ofprocesses through which all carbonatoms rotate.

Carbon exists in Earth’s atmosphereprimarily as carbon dioxide.

All green plants contain chlorophyll, apigment that gives them theircharacteristic color. Duringphotosynthesis, chlorophyll trapsenergy from sunlight and uses it toconvert carbon dioxide and water intoglucose and oxygen.

Carbon is transferred from greenplants to animals when animals eatplants or other animals.

All animals and plants need energy todrive their various metabolicprocesses. This energy is provided byrespiration. During this process,glucose reacts with oxygen to formcarbon dioxide and water. These wasteproducts are subsequently releasedinto the atmosphere. In essence,respiration is the opposite process tophotosynthesis.

When plants and animals die, theirbodies decompose. In the presence ofair, the carbon they contain becomescarbon dioxide, which is released intothe atmosphere.

When plants and animals decay in theabsence of air, carbon cannot beconverted into carbon dioxide.Instead, it remains and forms fossilfuels such as coal, crude oil, andnatural gas.

When fossil fuels are burned, thecarbon they contain becomes carbondioxide and is released into theatmosphere.

a aa a aaaaaaa aaaaaaaaaa a aaaa a a a aaaaaaa aaaaaaaa carbon dioxide in the airb sunlightc plants take in carbon dioxide and give out oxygend animals take in oxygen, eat plants and vegetables, and breath out CO2e death and decayf carbon compounds (e.g., in oil and coal)g burning fuel produces CO2

Respiration

glucose+oxygen→ +water+energy

C6H12O8(aq) + 602(g) → 6CO2(g) + 6H2O(I)

Photosynthesis

+water glucose+oxygencarbondioxide chlorophyll

sunlightcarbondioxide

6CO2(g) + 6H20(I) → C6H12O6(aq) + 6O2(g)

ab

c

d

g

e

f

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CHEMISTRY OF CARBON

151

carbonatecarbon dioxidecarbon monoxide

Key words

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1 Preparation of carbon dioxide

2 Preparation of dry carbon dioxide

a b

c

d

e

f e

3 Preparation of carbon monoxide

a marble chipsb dilute hydrochloric acidc carbon dioxided watere carbon dioxide

f concentrated sulfuric acidg ethanedioic (oxalic) acid crystals and concentrated sulfuric acidh heati concentrated potassium hydroxide solutionj carbon monoxide

g

h

j

i

Carbon oxides The most common forms of carbon

oxides are carbon dioxide, which isinstrumental in the carbon cycle, andcarbon monoxide, a colorless,odorless gas that is the result of theincomplete combustion of fuels. Theycan be prepared in the laboratoryusing the following techniques.

1 Carbon dioxide Carbon dioxide is formed when a

metal carbonate reacts with a diluteacid:metal carbonate + dilute acid

metal salt + carbon dioxide + water

When calcium carbonate (marblechips) reacts with dilute hydrochloricacid:CaCO3(s) + 2HCl(aq)

CaCl2(aq) + CO2(g) + H2O(l)

Carbon dioxide is not very soluble inwater, so it can be convenientlycollected over water.

2 Dry carbon dioxide Carbon dioxide can be dried by

passing it through concentratedsulfuric acid and collected bydownward delivery (upwarddisplacement) because it is denserthan air.

3 Carbon monoxide Carbon monoxide is formed by the

dehydration of ethanedioic (oxalic)acid using concentrated sulfuric acid:

conc. sulfuric acid

HOOC-COOH(l) ——————————

CO2(g) + CO(g) + H2O(l)

Acid residues and carbon dioxide areremoved by passing the gas through apotassium hydroxide solution. Carbonmonoxide can be collected over waterbecause it is only slightly soluble.

Laboratory preparationof carbon oxides

The fractional distillationof crude oil

CHEMISTRY OF CARBON

152

fractionaldistillation

hydrocarbon

Key words

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1 Fractional distillation of crude oil

2 Crude oil composition (percent yields and uses of oil)

a

b

c

d

g

h

j

k

l

e

f

i

j

k

l

i

j

k

l

i

a crude oilb heaterc bubble capd refinery gase gasoline (110°C)f kerosine (180°C)

g diesel oil (260°C)h residue — bitumen tar (400°C)i gasoline and chemical feedstockj kerosinek gas oill fuel oil

Arabianheavy

Iranianheavy

Arabianlight

18%

11.5%

18%

52.5%

21%

13%

20%

46%

21%

15%

21%

43%

Fractional distillation Fractional distillation is one of

several processes used to refine crudeoil. Refining converts crude oil into arange of useful products.

Crude oil is a complex mixture ofhydrocarbons. During fractionaldistillation, this mixture is separatedinto a series of fractions (components)on the basis of boiling point.

The crude oil is passed through afurnace, where it is heated to 400°Cand turns mostly into vapor. The gasespass into a distillation column withinwhich there is a gradation oftemperature. The column is hottest atthe bottom and coolest at the top.

Hydrocarbons with the highest boilingpoints are the first to condense at thebottom of the column, along with anyremaining liquid residue from thecrude oil. This fraction providesbitumen for use in road building.

Rising up the column, other fractionscondense out: first diesel oil, thenkerosene, and finally gasoline. All ofthese fractions are used as fuels.

The hydrocarbons with the lowestboiling points remain as gases and riseto the top of the column. This fractionis used as a fuel in the refinery.

The hydrocarbon vapor moves up thecolumn through a series of bubblecaps. At each level, the hydrocarbonvapor passes through condensedhydrocarbon liquid. This helps toensure a good separation into thevarious fractions.

Crude oil composition Crude oil varies in composition,

depending on where it was obtained.Fractional distillation of different crudeoils provides different proportions ofthe various fractions.

alkanealkenecatalytic crackingfractional

distillation

isomerizationpolymerizationreformingresidfining

CHEMISTRY OF CARBON

153

Other refining processesKey words

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1 Other processes Other refining processes are used to

modify the products of fractionaldistillation. These includeisomerization, reforming, catalyticcracking, polymerization, andresidfining.

2 Isomerization Isomerization changes the shape of

hydrocarbon molecules. For example,pentane is converted into 2-methlybutane.

3 Reforming Reforming converts straight chain

molecules into branched molecules inorder to improve the efficiency ofgasoline. One type of reaction involvesthe dehydration of saturatedcompounds to unsaturatedcompounds. Another involves thecyclization of hydrocarbons.

4 Catalytic cracking In general, smaller hydrocarbon

molecules, such as those in gasoline,are in greater demand than largerones. Catalytic cracking redresses thisbalance by breaking (cracking) largealkane molecules into smaller alkaneand alkene molecules.

5 Polymerization Polymerization combines small

molecules to form larger moleculesthat can be used to make variousproducts.

Residfining Resifining is the process used on the

residue fraction to convert it intousable products. It also removesimpurities that would damage thecatalyst used in catalytic cracking.

4 Catalytic cracking

Octane propane and pent-1-ene

CH3CH2CH2CH2CH2CH2CH2CH3 CH3CH2CH3 + CH3CH2CH2CH=CH2octane propane pent-1-ene

5 Polymerization

Two propene molecules combine to form hexene

CH3CH=CH2 + CH3CH=CH2 CH3CH2CH2CH2CH=CH2propene propene hex-1-ene

1 Other refining processes

isomerization reforming residfiningcatalyticcracking

polymerization

fractional distillation

2 Isomerization

3 ReformingDehydration

Cyclization

CH3—CH2—CH2—CH2—CH2—CH3 CH3—CH2—CH2—CH—CH3

CH32-methylbutanepentane

CH3

CH

CH2CH2

CH2CH2

CH2

CH3

C

CHCH

CHCH

CH

+ 3H2

methylbenzenemethylcyclohexane

CH3—CH2—CH2—CH2—CH2—CH2—CH3

CH3

CH

CH2CH2

CH2CH2

CH2

methylcyclohexane

heptane

Carbon chainsCHEMISTRY OF CARBON

154

alkanealkenealkynebondcarbon

catenationvan der Waals

forces

Key words

1 Catenation Carbon has the ability to form long

chains of carbon atoms in itscompounds. This is called catenation.

2 Melting and boilingpoints Forces of attraction, called van der

Waals forces, exist between molecules.As molecular size increases, there ismore overlap between the molecules,and the intermolecular forces ofattraction increase.

In order to melt and to boil, the forcesof attraction between molecules mustbe overcome. The greater theseforces, the more energy is needed.This is reflected in a steady increase inmelting point and boiling point asmolecules increase in size.

3 Types of bonds A carbon atom may form one, two, or

three bonds with another carbon atomin its compounds. These bonds aredescribed as single bonds (C–C),double bonds (C=C), and triple bonds(C[C).

Alkanes contain only carbon–carbonsingle bonds.

Alkenes contain a carbon–carbondouble bond.

Alkynes contain a carbon–carbon triplebond.

Alkanes, alkenes, and alkynes are allhydrocarbons since they consist onlyof hydrogen and carbon atoms.

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–187 –94 18

–41 69 287

1 Catenation

H C C C C C C C C H

H H H H H H H H

H H H H H H H H

H C C H H C C C H

H H H H H

H H H H H

2 3 8Chain length

3 6 16Chain length

H C C C C C C H

H H H H H H

H H H H H H

H C C C H

H H H

H H H

C16H34

m.p./°C

b.p./°C

H C C H

H H

H H

2 Melting and boiling points of some chains

3 Types of bonds

C CH

H

H

H

H C C

C C

Double bond

C C

Single bond

C C

Triple bond

H

Alkanes

Alkenes

Alkynes

C3H8 C6H14

CHEMISTRY OF CARBON

155

Naming hydrocarbonsalkanealkenealkynefunctional grouphydrocarbon

Key words

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Naming hydrocarbons The name of a hydrocarbon indicates

the number of carbon atoms in themolecule and what sort ofcarbon–carbon bonds is present.

1 Chain length The first part of name is determined

by the number of carbon atoms in themolecule. The same prefixes are usedfor all groups of organic compounds.

2 Functional group The second part of the name is

determined by the type ofcarbon–carbon bonds present. Eachfunctional group has a unique suffix.

The position of the functional group ina carbon chain is identified bynumbering the carbon atoms in thecarbon chain.

3 Examples of compoundnames The first two examples in the diagram

are alkanes. If there is one carbonatom in the molecule it is:“meth” (1 carbon atom in the chain) + “ane” (for alkane): methane.If there are four carbon atoms in themolecule it is:“but” (4 carbon atoms in the chain) + “ane” (for alkane): butane.

The third example is propane, analkene with three carbon atoms:“pro” (3 carbon atoms in the chain) + “ene” (for alkene).

The fourth example is ethyne, analkyne with a two carbon chain:“eth” (2 carbon atoms in the chain) + “yne” (for alkyne).

Chain length

First part of name

C1

meth-

C2

eth-

C3

prop-

C4

but-

C5

pent-

C6

hex-

Second partof name

Functional group

-ane -ene -yne

Molecule Chain length Functional group Name

1 meth- -ane methane

4 but- -ane butane

3 prop- -ene propene

2 eth- -yne ethyne

Alkane Alkene Alkyne

1 Chain length gives first part of name

2 Functional group gives second part of name

3 Examples of organic compound names

C H

H

H

H C H

H

H

H C C C

H H H

H H H

H C C

H

H H

C H

H

C CH

H

C C

C H

H

H

C H

H

H

C C

C C

C C

C H

H

H

H

Table of the first sixalkanes

CHEMISTRY OF CARBON

156

alkanehomologous

serieshydrocarbon

van der Waalsforces

Key words

The first six alkanes The alkanes form an homologous

series of compounds that have thegeneral formula CnH2n+2, where n is apositive integer. Each alkane moleculediffers from the previous one in theseries by -CH2-.

They have similar chemical propertiesand show a gradation of physicalproperties, such as melting point andboiling point, as the molecular sizeincreases.

Alkane molecules are attracted to eachother by van der Waals forces. Asmolecular size increases, there is moreoverlap between the molecules, andthe intermolecular forces of attractionincrease.

Alkane molecules are frequentlyshown as having a flat two-dimensionalstructure because this is easy to draw,but in reality, the four bonds aroundeach carbon atom are directed towardthe corners of a tetrahedron. Theangle between any two bonds is109.5°.

Alkanes are relatively unreactivesubstances when compared with othergroups of hydrocarbons. Their mostimportant reaction is combustion, andthey are the main constituent of arange of fuels. Natural gas is largelycomposed of methane:CH4 + 2O2 CO2 + 2H2O

In a good supply of air, hydrocarbonsburn to give carbon dioxide and water.In a restricted supply of air, carbonmonoxide and/or carbon may beformed:C2H6 + 2O2 CO + C + 3H2O

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Structuralformula

Structuralformula

MethaneAlkane

Formula

Boilingpoint (°C)

Physicalstate at roomtemperature

Molecularmodel

Ethane Propane

Formula

Boilingpoint (°C)

Physicalstate at roomtemperature

Molecularmodel

C6H14C5H12C4H10

C3H8C2H6CH4

LiquidLiquidGas

Gas Gas Gas

–164 –87 –42

0 36 69

H C C C C C C H

H H H H H H

H H H H H H

H C C C C C H

H H H H H

H H H H H

H C C C C H

H H H H

H H H H

H C H

H

H

H C C H

H H

H H

H C C C H

H H H

H H H

Butane Pentane HexaneAlkane

CHEMISTRY OF CARBON

157

Table of the first fivealkenes

addition reactionalkenefunctional grouphomologous

series

van der Waalsforces

Key words

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The first five alkenes The alkenes form an homologous

series of compounds with the generalformula CnH2n, where n is a positiveinteger. Each alkene molecule differsfrom the previous one in the series by-CH2-.

Alkene molecules are attracted to eachother by van der Waals forces. Asmolecular size increases, there is moreoverlap between the molecules, andthe intermolecular forces of attractionincrease. The series thus shows agradation of physical properties, suchas melting point and boiling point.

Alkenes all contain the samefunctional group, a carbon–carbondouble bond, represented by C=C.

The bonds around each of the carbonatoms in a carbon–carbon doublebond are in the same plane anddirected toward the corners of anequilateral triangle. The angle betweenany two bonds is 120°.

Alkenes undergo combustion in thesame way as alkanes. However, theyhave other chemistry resulting fromthe reactive carbon–carbon doublebond.

Alkenes undergo addition reactions inwhich a molecule is added across thecarbon–carbon double bond. Forexample, ethene undergoes thefollowing addition reactions:CH2=CH2 + H-H CH3-CH3

ethene + hydrogen ethane

CH2=CH2 + H-OH CH3-CH2-OH

ethene + steam ethanol

CH2=CH2 + H-Br CH3-CH2Br

ethene + hydrogen bromide

bromoethane

CH2=CH2 + Br-Br CH2Br-CH2Br

ethene + bromine 1,2-dibromoethane

Str

uctu

ral

form

ula

HC

C

HH

H

CC

Eth

ene

Alk

ene

Form

ula

Boi

ling

poin

t(°

C)

Phy

sica

lst

ate

atro

omte

mpe

ratu

re

Mol

ecul

arm

odel

Pro

pene

But

ene

C4H

8

C3H

6

Gas

Gas

Gas

–10

4

–47

–6

Num

ber

ofca

rbon

atom

spe

rm

olec

ule

2 3 4

C2H

4

C

HC

C

HH

HH

CCH

C6H

12

C5H

10

65C

CC

HH

HH

CCH

H H

H30 64

H HH H

H H

H H H H

Liqui

d

Liqui

d

Pen

tene

Hex

ene

CC

C

HH

HH

CCH

H H

H H

HC

H H

EtheneCHEMISTRY OF CARBON

158

alkeneethaneetheneethanol

geometricisomerism

halogensisomer

Key words

Ethene Ethene is the first member of the

alkene series. It is a colorless,flammable gas.

1 Preparation In the laboratory, ethene can be made

by the dehydration of ethanol usingconcentrated sulfuric acid.

2 Structure Ethene, like all alkenes, contains a

carbon–carbon double bond aboutwhich rotation is impossible.

3 Isomerism Isomers are compounds having the

same molecular formula and relativemolecular mass but different three-dimensional structures.

The existence of two compounds withthe same molecular formula but wheregroups are distributed differentlyaround a carbon–carbon double bondis described as geometric isomerismor cis / trans isomerism.

The prefix “cis” is used when thesubstituent groups (an atom or groupof atoms substituted in place of ahydrogen atom or chain) of ahydrocarbon are or the same side of aplane through the carbon–carbondouble bond. The prefix “trans” isused when the substituent groups areon the opposite side.

In trans-1,2-dibromoethene thebromine atoms are on opposite sidesof a plane through the carbon–carbondouble bond.

In cis-1,2-dibromoethene the bromineatoms are on the same side.

4 Reactivity The carbon–carbon double bond in

ethene is very reactive and willundergo various addition reactions.Ethene reacts with: halogens (such aschlorine) to form 1,2-dihaloethane,hydrogen to form ethane, andhydrogen halides to form haloethane.©D

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1 Dehydration of ethanol to produce ethenea concentrated sulfuric acidb ethanolc heatd alkali — to remove impuritiese waterf ethene

2 Structure

a

b

c d

e

f

4 Reactivity

C CH H

H HC C

H Br

Br HC C

H H

Br BrEthene Trans-1, 2-dibromoethene Cis-1, 2-dibromoethene

3 Isomerism

Ni

CH3CH2OH CH2=CH2

-H2O

ethanol ethene

Reaction with hydrogen halides to form haloethane

CH2 = CH2 + HX CH3CH2X

Reaction with hydrogen to form ethane

CH2 = CH2 + H2 CH3CH3

CH2 = CH2 + Cl2 CH2Cl—CH2ClReaction with chlorine to form 1, 2-dichloroethane

CHEMISTRY OF CARBON

159

Polymersaddition

polymerizationbakeliteethene

polyethenepolymerpolymerization

Key words

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Polymers A polymer is a large organic molecule

composed of repeating carbon chains.The physical properties of a polymerdepend on the nature of these carbonchains and how they are arranged.

1 Types of branching A certain amount of side branching

occurs during polymerization,depending on the reaction conditions.

Low pressure and low temperatureresults in a high-density polymer.

Very high pressure and moderatetemperatures produce a low-densitypolymer.

In high-density polymers, the carbonchains are unbranched, and they canbe packed closely together forming adense substance, e.g., high-densitypolyethene (1A).

In low-density polymers, the carbonchains are branched, and it is notpossible to pack them as closelytogether, e.g., low-density polyethene(1B).

In polymers like bakelite, there arecross links between the carbon chains,producing a hard, rigid structure (1C).

2 Addition polymerization Ethene forms a polymer by a process

called addition polymerization. In this process, one of the bonds from

the carbon–carbon double bond isused to form a bond with an adjacentmolecule. This process is repeatedmany times, resulting in long chainscontaining thousands of carbon atoms.

Polymer with few branched chains,e.g., high-density polyethene

Polymer with many branched chains,e.g., low-density polyethene

Polymer with much cross-linking,e.g., bakelite

1 Types of branching

2 Additional polymerization (illustrating how ethene can berestructured to form poly(ethylene) i.e., polyethene)

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

H

C C

H H

H H

C C

H H

H H

C C

H H

H H

C C C C C C

H H H H H H

H H H H H H

A

C

B

Polymers: formationCHEMISTRY OF CARBON

160

alkenemonomer

polymer

Key words

Monomers Monomers are the basic units from

which a polymer is made. The systematic name for a polymer is

derived from the name of themonomer. For example, polypropeneis “poly” (for polymer) + the alkenepropene.

The diagrams at right illustrate theformation of some alkene polymers.

1 Forming polypropene Propene molecules combine to form

polypropene. Most polypropene is produced as a

monopolymer (a polymer formedfrom propene only).

2 Formingpolychloroethene Chloroethene molecules combine to

form polychloroethene. 1,2-dichloroethane is made by

chlorinating ethene. This product isthen cracked to form chloroethene.

3 Formingpolyphenylethene Phenylethene molecules combine to

form polyphenylethene. Phenylethane is made from ethene

and benzene by a Friedel-Craftsreaction using aluminum(III)chloride/hydrochloric acid catalyst.This is dehydrogenated to give thephenylethene monomer.

4 Formingpolytetrafluoroethene Tetrafluoroethene molecules combine

to form polytetrafluoroethene. Trichloromethane is produced by the

reaction of methane with controlledamounts of chlorine/hydrochloric acid.This is reacted with anhydroushydrogen fluoride in the presence ofantimony(III) chloride to givechlorodifluoromethane, which issubsequently cracked to producetetrafluoroethene.

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C C

H

H

Cl

H

1 Restructuring of propene to make poly(propene)

2 Restructuring of chloroethene to make poly(chloroethene) i.e., polyvinylchloride

C C C C C C

CH3 H H H

H H H H H H

CH3 CH3

C C C C C C

Cl H H H

H H H H H H

Cl Cl

C C

H

H

Cl

H

3 Poly(phenylethene)

C C

C6H5 H

H H

C C

H

H

C6H5

H

C C

H

HH

C C

H

HH

C6H5 C6H5

C C

C6H5 H

H H

C C

C6H5 H

H H

4 Poly(tetrafluoroethene)

C C C C C C

F

F

C C

F

F

F

F

C C

F

F

F

F

C C

F

F

F

F

F F F F F

F F F F F

C C

H

H

CH3

H

C C

H

H

CH3

H

C C

H

H

CH3

H

C C

H

H

Cl

H

C C

H

H

Cl

H

CHEMISTRY OF CARBON

161

Polymers: table ofproperties and structure

monomerpolymerpolymerization

Key words

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Polymers Most polymers have common names

that are used in everyday language. The uses of polymers depend on their

properties.

Classification There are several ways in which

polymers can be classified. Heat. Thermoplastics soften when

heated and harden on cooling, so theycan be reshaped many times withoutchanging their chemical structure.Thermosets are chemically altered onheating and produce a permanentlyhard material that cannot be softenedby heating.

Method of polymerization. Additionpolymers are usually formed frommonomers containing a –CH=CH- unitto which different atoms or groups areattached. On polymerization, one ofthe carbon–carbon bonds becomes abond to another unit. Condensationpolymers are formed fromcondensation reactions in which asmall molecule, sometimes but notalways water, is lost.

Formula. Homopolymers are formedfrom one monomer unit. Co-polymersare formed from two or moremonomers.

Chemical structure. Linear chains mayhave straight, zigzag, coiled, orrandom spatial arrangements.Branched chains have side branchchains attached to the main chains.Cross-linked chains have two or threedimensional cross-linkage betweenchains.

Steric structure. Isotactic: in which allside groups are on the same side ofthe main chain. Syndiotactic: in whicheach alternative side group has thesame orientation. Atactic: in whichthere is no specific pattern to thedistribution of side groups.

Pol

ymer

syst

emat

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me

Pol

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com

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nam

eP

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ses

Str

uctu

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mon

omer

CC

H

HH

C6H

5

CC

F F

F F

CC

H HHH

CC

H

HCH

3

H

CC

H

HCl

H

CC

H

HCH

3

H

OC

H3

O

CC

H

HH

CN

Pol

y(et

hene

)

Pol

y(pro

pane

)

Pol

y(ch

loro

ethe

ne)

Pol

y(phe

nyle

then

e)

Pol

y(et

hene

)

Pol

y(m

ethy

l-2-

met

hyl-

pro

pen

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)

Pol

y(pro

pen

enit

rile

)

Pol

yeth

ene

Pol

ypro

pyle

ne

PV

C(p

olyv

inyl

chlo

ride)

Pol

ysty

rene

PTFE

(pol

ytet

rafluo

roet

hene

)

Per

spex

Acr

ilan

low

den

sity

;hi

ghden

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high

den

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flex

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and

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CHEMISTRY OF CARBON

162

alcoholalkenecarboxylic acidesterfunctional group

homologousseries

oxidation

Key words

Functional groups A functional group is the atom or

group of atoms present in a moleculethat determines the characteristicproperties of the molecule.

A homologous series is a group ofcompounds that contain the samefunctional group. The physicalproperties of a homologous seriesshow a gradation as molecular sizeincreases. The chemical properties of ahomologous series are similar becausethey are determined by the functionalgroup.

1 Alkenes Alkenes contain the functional group

C=C. Their general formula is CnH2n. Alkenes are reactive and undergo

additional reactions.

2 Alcohols Alcohols contain the functional group

C-OH. Their general formula is CnH2n+1OH. Alcohols can also undergo oxidation

to give carboxylic acids, or they can bedehydrated to alkenes. They can alsoreact to form ester compounds

3 Carboxylic acids Carboxylic acids contain the

functional group -COOH. Carboxylic acids are typically weak acids

that partially dissociate into H+ cationsand RCOO- anions in aqueous solution.

Carboxylic acids are widespread innature.

4 Esters Esters contain the functional group

–COOC-. Esters are formed by a reaction

between a carboxylic acid and analcohol.

Esters are used in flavorings andperfumes.

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Functional group

1 Alkenes

2 Alcohols

3 Carboxylic acids

H C C O

H H

H H

C CC H

H HH

HH

C C

H

C O

H

O

CC

H

H HO H

O

CO H

4 Esters

O

CO H

Propene

Ethanol

Ethanoic acid

Methylethanoate

H C C

H

H

O

O C H

H

H

Example

Functional groups andhomologous series

CHEMISTRY OF CARBON

163

Alcoholsalcoholalkanefunctional grouphydrogen bond

Key words

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1 Naming Alcohols are named by dropping the

terminal “e” from the alkane chainand adding “ol.” For example,methane is the alkane; methanol is thealkanol, or alcohol. When necessary,the position of the hydroxyl (-OH)group is indicated by a numberbetween the alkane name and the “ol,”e.g., propan-1-ol, or in front of thename, e.g., 2-propanol.

2 Classification Alcohols may be classified as primary,

secondary, or tertiary on the basis ofthe number of carbon atoms bondedto the carbon carrying the functionalgroup (-OH).

3 Sharing of electrons An oxygen atom is more

electronegative than a hydrogen atom,and this leads to an unequal sharing ofthe electrons in the O-H bond. Thebonding electrons are drawn moretoward the oxygen atom and, becausethe electrons carry a negative charge,the oxygen atom becomes slightlynegative. This is described as deltaminus and is denoted by d-.Conversely, the hydrogen atombecomes slightly positive—delta plus,denoted by d+. (R represents thecarbon group attached to the oxygen.)

4 Hydrogen bonding The -OH functional group generally

makes the alcohol molecule polar. Ithas a positive charge at one end and anegative at the other. Molecules canform hydrogen bonds with oneanother and other compounds whenthe oppositely charged parts areattracted to each other, forminghydrogen bonds.

CH3-OH methanol

CH3CH2-OH ethanol

CH3CH2CH2-OH propan-1-ol

CH3CH2CH2CH2-OH butan-1-ol

CH3CH2CH2CH2CH2-OH pentan-1-ol

CH3CH2CH2CH2CH2CH2-OH hexan-1-ol

1 The first six alcoholsStructure

2 Classification

Primary alcohol Secondary alcohol Tertiary alcohol

R Od-

Hd+

R O

H

O

H

R

4 Hydrogen bonding

3 Sharing of electrons

Name

H C C OH

H

H H

H

H C C C

H

H OH

H

H

H

H H C C C

H

H OH

H

H

H

H

HH

H

Carboxylic acidsCHEMISTRY OF CARBON

164

alkalicarbonatecarboxylic aciddissociationhomologous

series

pHsalt

Key words

1 Naming Carboxylic acids are named by adding

the suffix “anoic acid” to the prefixesused for all homologous series oforganic compounds. For example, thecarboxylic acid containing threecarbon atoms is “prop” + “anoic acid”= “propanoic acid.”

2 Hydrogen bonding Hydrogen bonding is present between

carboxylic acid molecules, resulting inhigher boiling points than mightotherwise be expected and miscibilitywith water.

3 Ionization Carboxylic acids ionize to give

hydrogen ions, H+; however, they areweak acids because they are onlypartially ionized.

The dissociation constant for ethanoicacid, for example, is 1.75 x 10-5

mol3dm-6. This means that only about4 molecules in every 1,000 are ionizedat any one time.

Characteristics Carboxylic acids have a pH value of

approximately 3–5. Carboxylic acids react with carbonates

and hydrogencarbonates to producecarbon dioxide:2H+(aq) + CO3

2-(aq)

H2O(l) + CO2(g)

H+(aq) + HCO3-(aq)

H2O(l) + CO2(g)

Carboxylic acids form salts withalkalis:CH3COOH(aq) + NaOH(aq)

ethanoic acid sodium hydroxide

CH3COO-Na+(aq) + H2O(l)

sodium ethanoate water

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+

CHOOH methanoic acid

CH3COOH ethanoic acid

CH3CH2COOH propanoic acid

CH3CH2CH2COOH butanoic acid

CH3CH2CH2CH2COOH pentanoic acid

CH3CH2CH2CH2CH2COOH hexanoic acid

1 The first six carboxylic acidsStructure

R C

O

3 Ionization

2 Hydrogen bonding

O

H O

H

C O

R

R C

O

O

R C

O

O

H

Name

CHEMISTRY OF CARBON

165

Estersalcoholalkylarylcarboncarboxylic acid

esterfunctional groupsaponification

Key words

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Esters Esters contain the functional group

–COOR, where R is an alkyl or an arylgroup.

1 Forming esters Esters are formed by the reaction of

carboxylic acids with alcohols in thepresence of a strong acid catalyst, suchas concentrated sulfuric acid. Thereaction involves the loss of water.

Esters generally have a fruity smell thatcan be used to identify their presence.They are used for food flavorings andin cosmetics.

Esters have no –OH group, so theycannot form hydrogen bond likecarboxylic acids and alcohols.Consequently, they are more volatileand are insoluble in water.

2 Naming The name of an ester is derived from

the carboxylic acid and the alcoholfrom which it is formed.

The alcohol part of an ester is writtenat the beginning of the ester name;from methanol we get methyl, fromethanol we get ethyl, etc.

The acid part of an ester is written atthe end of the ester name. It is writtenas if it was an ionic carboxylate groupin a salt; from ethanoic acid we getethanoate, from propanoic acid we getpropanoate, etc.

3 Saponification When esters are heated with an alkali,

such as sodium hydroxide, they arereadily hydrolyzed to form an alcoholand a carboxylic acid salt.

This may be described as asaponification reaction. It isimportant in the production of soapsfrom fats and oils.

1 Forming esters

H C C

C

H

H

H

H

R C

O

OH + H O R´ H2O

R C

O

O R´

concentratedsulfuric

acid

O

O

H

Structure of ester Name of ester

methyl ethanoate

ethyl ethanoate

propyl ethanoate

methyl propanoate

H C C

C C

H

H H

H

H H

O

O

H

H C C

C C C

H

H H

H

H H H

Cl

O

O

H

H C C

CH3

H

H O

O

C

H

H

3 Saponification

R C

O

O R´

R C

O

O–

+

Na+

R´+ OH

2 Naming

NaOH

Soaps and detergentsCHEMISTRY OF CARBON

166

carboxylic aciddetergentesterfatty acidhydrophilic

hydrophobicsoap

Key words

Soaps and Detergents Soaps are cleansing agents made from

fatty acids derived from natural oilsand fats. Detergents are made fromsynthetic chemical compounds.

1 Fatty acids Carboxylic acids occur in animal and

plant fats and oils. They may containfrom 7 to 21 carbon atoms and areoften referred to as fatty acids.

2 Making soap Most naturally occurring fats and oils

are esters of propane-1,2,3-triol(glycerine). When the fats are boiledwith sodium hydroxide, propane1,2,3,-triol and a mixture of sodium salts ofthe three carboxylic acids are formed.These salts are what we call soaps.

3 Soap molecule One end of a soap molecule is ionic,

while the other end is covalent. Theionic end is described as hydrophilicbecause it dissolves in water.Conversely, the covalent end isdescribed as hydrophobic because itdoes not dissolve in water, but it willdissolve in organic substances like oils.

4 Cleaning action The cleaning action of soap is the

result of the different affinities of thetwo ends of the soap molecule.

The hydrophobic end of the moleculedissolves in oils and fats on the fabric,while the hydrophilic end of themolecule remains in the water.

The oil and fat particles are lifted offthe fabric and held in the water bysoap molecules.

5 Detergent molecule Alkylbenzene sulfonates are common

examples of detergents.

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waterwater

1 Common fatty acids

2 Making soap

5 Detergent molecule

3 Soap molecule

4 Cleaning action

Name Formula Found in

palmitic acid CH3(CH2)14COOH animal and vegetable fats

stearic acid CH3(CH2)16COOH animal and vegetable fats

oleic acid CH3(CH2)7CH=CH(CH2)7COOH most fats and oils

linoleic acid CH3(CH2)4CH=CHCH2CH= soya-bean oil and nut oil

CH(CH2)7COOH

CH2—O—C—R´

O

CH —O—C—R´

O

CH2—O—C—R´´

O

+ 3NaOH

CH2—OH + R´ —C—O–Na+

CH —OH + R´ —C—O–Na+

CH2—OH + R´´—C—O–Na+

O

O

O

H—C—C—C—C—C—C—C—C—C—C—C—C—C—C—C—CO

O–Na+

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H—C—C—C—C—C—C—C—C—CC—CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H C==CC—S—O–Na+

O

OHH

NaOC==O C ==

OC

ONa

C ==O

ONa

C ==O

ONaNaO

==O

fabric

oil

CHEMISTRY OF CARBON

167

alkanealkenehomologous

series

Key words

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Physical properties All homologous series of compounds

show a gradation of physicalproperties as the carbon chain lengthincreases.

Alkanes The simplest alkane is CH4, methane.

The next simplest alkane is the twocarbon alkane, ethane (C2H6). Both ofthese are gases.

The five carbon alkane, pentane(C5H12), is a liquid.

The 34 carbon compound, butadecaneis a solid.

Alkenes The simplest alkene is the two carbon

alkene, ethene (C2H4), which is a gas. 2-pentene (C5H10), which is a five

carbon alkene, is a liquid. 2-butedecane, which is a 34 carbon

alkene, is a solid.

C C

H H

H H

H C C C

H H

H H

C C

H H

H H

H

H

H

C C (CH2)30

H

H

C C

H

H

H

H C C (CH2)30

H H

H H

C C

H H

H H

H

Alkanes

Alkenes

H C C C

H H H

H H H

C C

H H

H H

H

H C C H

H H

H H

ChainlengthC2,

ChainlengthC5,

ChainlengthC34,

ChainlengthC2,

ChainlengthC5,

ChainlengthC34,

Gas

Liquid

Solid

Gas

Liquid

Solid

Organic compounds:states

Functional groups andproperties

CHEMISTRY OF CARBON

168

alcoholaldehydealkenecarboxylic acidester

functional grouphomologous

seriesketonepolymer

Key words

Functional groups andproperties All members of an homologous series

of compounds has the samefunctional group. Because thefunctional group determines most ofthe chemistry of a compound,members of a particular homologousseries will have similar chemicalreactions.

Alkenes are unsaturated compoundsbecause they all contain acarbon–carbon double bond thatmakes them very reactive. Typically,they will undergo addition reactionswith hydrogen, halogens, and water.They also form a variety of polymers.

Alcohols with a small relativemolecular mass are flammable liquidsand readily dissolve in water. Primaryalcohols are readily oxidized: first toaldehydes and then to carboxylicacids. Secondary alcohols are oxidizedto ketones:

[O] [O]

R-CH2-OH R-CHO

R-COOH

primary alcohol aldehyde

carboxylic acid

[O]

R-CHOH-R R-CO-R

secondary alcohol ketone

Carboxylic acids are weak acids sincethey only partially ionize. They havesimilar reactions to fully ionizedmineral acids but they react with lessvigor. Sodium salts of carboxylic acidsare ionic compounds. Those withshort carbon chains are readily solublein water.

Esters are volatile liquids or low-melting solids. They are usuallyinsoluble in water but soluble inethanol and diethyl ether. Esters havesweet fruity smells and are used inperfumes, flavorings, and essences.

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H C C

Hconc

H H

OH

Class ofcompound

Alkene

ExampleFunctional

group

Alcohol

Carboxylicacid

Ester

O

H C H

H

O C H

O

C

O C

H

H C C

H

H O H

H

C

O H

C C

H H

H

H C C

H H

OH

H

C O

Typical chemical propertyClass ofcompound

Alkene

Alcohol

Carboxylicacid

Ester

Ethene

Ethanole

Ethanoic acid

Methyl methanoate

C C

H H

C C

Br Br

+Br2

C C

H

H H

H

C C

H

H H

HH

H2SO4

Decolorizes bromine water

Decolorizes bromine water

Reacts with sodium carbonate solution

Can be hydrolized by alkali

2CH3COOH + Na2CO3 2CH3COO–Na+ + CO2 + H2O

HCOOH3 + NaOH HCOO–Na+ + CO3OH

CHEMISTRY OF CARBON

169

Reaction summary:alkanes and alkenes

additionpolymerization

alkanealkenesolvent

Key words

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Reaction of alkanes andalkenes Both alkanes and alkenes burn readily

in a good supply of air to producecarbon dioxide and water.

Crude oil is a complex mixture ofalkanes, which are separated intofractions (components) on the basis ofboiling point during the refiningprocess. Some of these fractionsprovide gasoline, diesel, aviation fuel,and fuel oil.

The quality of gasoline (how smoothlyit burns) in indicated by its octanenumber, which ranges from 0–100: thehigher the octane number thesmoother burning the gasoline. Theoctane number is the percentage byvolume of 2,2,4-trimethylpentane (alsoknown as iso-octane) in a mixture of2,2,4-trimethylpentane and heptane,which has the same knockingcharacteristics as the gasoline beingtested.

Historically, tetraethyllead(IV)Pb(C2H5)4 was added to gasoline as ananti-knock additive to make it burnmore smoothly. A growing knowledgeof the poisonous nature of lead hasresulted in the development of lead-free fuels in which other anti-knockadditives, such as MTBE (methyltert-butyl ether), are used.

Crude oil contains no alkenes, butthey are produced in cracking andother refining processes. Alkenes areimportant feedstock for additionpolymerization but are also used ingasoline blending, making plasticizers,and as solvents.

Much of the chemistry of the alkenesis the result of the reactive nature ofthe carbon–carbon double bond.Alkenes undergo addition reactionswith a variety of substances.

Alkanes

Combustion

Substitution

Cracking

C8H18 H2C = CH2 + C6H14

CH4 + Cl2 CH3Cl + HCl

C3H8 + 5O2 3CO2 + 4H2O

Alkenes

H2C = CH2 + H2 H3C – CH3

Hydrogenation

H2C = CH2 + Br2 H2C – CH2

Br Br

Substitution

nCH2 = CH2 (CH2 – CH2)n–

General reaction alkene to alkane

Reaction summary:alcohols and acids

CHEMISTRY OF CARBON

170

alcoholaldehydecarboxylic acidesterethanol

etheneoxidizing agent

Key words

1 Alcohols The majority of the world’s annual

production of ethanol is made by thecatalytic hydration of ethene.A mixture of ethene and steam at300°C and 70 atmospheres is passedover a phosphoric acid catalyst.

Ethanol is also made industrially bythe fermentation of carbohydrates.

It can also be prepared in thelaboratory using concentrated sulfuricacid and heat.

Ethanol burns readily in air. In somecountries it is used as a blending agentin motor fuels.

Alcohols can be oxidized to carboxylicacids by heating with a suitableoxidizing agent such as acidifiedpotassium dichromate. The oxidationinvolves two stages and goes via agroup of compounds called aldehydes.Under suitable conditions, the ethanalcan be removed from the reactionmixture before it is further oxidized toethanoic acid.

2 Acids Salts of short-chain carboxylic acids,

like sodium ethanoate, are ioniccompounds and are soluble in water.

Ethanoic acid and ethanol react in thepresence of a concentrated sulfuricacid catalyst to form the ester ethylethanoate. This reaction is reversed byheating ethyl ethanoate with an alkalisuch as sodium hydroxide solution.The sodium salt formed, sodiumethanoate, can be neutralized by dilutemineral acid to regenerate ethanoicacid.

esterification

ethanoic acid + ethanol

ethyl ethanoatehydrolysis

ethyl ethanoate

ethanoic acid + ethanol

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Alcohols

Preparation in industry

Fermentation

Preparation in the laboratory

Oxidation by burning

Oxidation by oxidizing agent

Reaction to produce an ester

CH3CH2OH + CH3CO2H H2O + CH3CO2CH2CH3conc

H2SO4

CH3CH2OH CH3 + COOHK2CR2O7 + dil H2SO4

CH3CH2OH + 3O2 2CO2 + 3H2O

CH2 = CH2 + H2O CH3CH2OHconc H2SO4

+ heat

C12H22O11 + H2O 2C6H12O6 4CH3CH2OH + 4CO2

enzyme

catalyst

enzyme

catalyst

CH2 = CH2 + H2O CH3CH2OHH3PO4 at 300°C

+70 Atmospheres

Organic acids

Reaction giving ionic salt

CH3CO2 + NaOH CH3COO–Na+ + H2O

Reaction giving covalent ester

CH3CO2 + CH3CH2OH CH3COOCH2CH3 + H2O

Reaction giving hydrolysis of an ester

CH3COOCH2CH3 + NaOH CH3COO–Na+ + CH3CH2OH

CHEMISTRY OF CARBON

171

Optical isomerismchiralenantiomeroptical isomerismracemate

Key words

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Optical isomerism Optical isomerism is a form of

isomerism in which two isomers arethe same in every way except that theyare mirror images that cannot besuperimposed on each other.

1 Chiral molecule When four different groups are

attached to a carbon atom, theresulting molecule has no symmetry.The molecule is said to be chiral, andthe carbon atom at the center isdescribed as asymmetric.

2 Enantiomers 1-bromo-1-chloroethane is a chiral

molecule. It exists in two forms, calledenantiomers, that differ only in theway that the bonds are arranged inspace.

The enatiomers of a chiral moleculeare mirror images of each other andcannot be superimposed on eachother.

3 Optical activity Chiral molecules are said to be

optically active since they rotate theplane of polarized light. If polarizedlight is passed through a solutioncontaining only one of theenantiomers, the plane of the light willbe rotated either to the right (dextro-rotatory) or to the left (laevo-rotatory).A similar solution containing only theother enantiomer will rotate the planeof the light by the same amount in theopposite direction.

A solution containing equal amountsof the enantiomers is called a racemicmixture or racemate. It is opticallyinactive since the two effects canceleach other out.

1 Chiral molecule

C

Br HCH3

Cl

C

BrHH3C

Cl

C

BrH

CH3

Cl

rotate

these are notthe same molecule

mirror

2 Enantioners

C

X ZY

W

Polarized

light

dextro-rotatory or (+) rotatory

laevo-rotatory or (–) rotatory

3 Optical activity

asymmetric carbon atom

CHEMISTRY OF CARBON

172

amineamino acidcarboxylic acidfunctional groupoptical isomerism

proteinzwitterion

Key words

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Amino acids and proteins

1 Amino acids Amino acids are compounds that

contain both amine (-NH2) and acarboxylic acid (-COOH) functionalgroups.

Amino acids are generally crystallinesolids that decompose on melting.They are soluble in water andinsoluble in organic solvents such asethanol.

2 Alanine Like most a-amino acids, alanine

contains an asymmetric carbon atomand exhibits optical isomerism. Thereare two forms of alanine; L-alanine andD-alanine (L=laevo-[left] rotatory;D=dextro-[right] rotatory.)

3 Zwitterions In aqueous solution, amino acids are

able to form ions that carry bothpositive and negative charge. Suchions are called zwitterions. They formby the loss of a proton from thecarboxylic acid group and the gain of aproton on the amine group.

4 Proteins Proteins are polymers consisting of

long chains of amino acids. The aminoacids join together forming peptidebonds by the loss of water:

-H2O

H2N-CHR-COOH + H2N-CHR-COOH

H2N-CHR-CONH-CHR-COOH

All of the amino acids in proteins arethe L-isomers.

4 Proteins

C

H2NH

COOH

CH3

C

H2N

H

CH3

COOHL-alanine D-alanine

H2N—CH—COOH

CH2

C O

NH2

asparagine

H2N—CH—COOH

CH2

COOH

aspartic acid

H2N—CH—COOH

H

glycine

H2N—CH—COOH

CH2

alanine

1 Amino acids

2 Alanine

H2N—CH—COOH

R

H2N—CH—COO–

R+

—H2N—CH—C

R O

HN—CH—C

R

peptide link

3 Zwitterions

CHEMISTRY OF CARBON

173

aldehydealdohexosealdoseanomerglucose

hexosemonosaccharide

Key words

6CH2OH

H—5C—OH

H—4C—OH

HO—3C—H

H—2C—OH

1CHO

6CH2OH

HO—5C—H

HO—4C—H

H—3C—OH

HO—2C—H

1CHO

L-glucoseD-glucose

6

4

2

3 1

5

β-D-glucose

32

5 5

32

4 41 1

6 6

β-D-glucoseα-D-glucose

CH2OH

OCH

OHOH

H

C C

CCOH

HH

OHH

OH

CH2OHHO

H

HOHHO

HO

HH

CH2OH

OCH OH

OH HC C

CCOH

HH

OHH

3 Hexagonal ring

1 Chain structure

2 Ring structure

Monosaccharides

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Monosaccharides Monosaccharides are simple sugars

that have between three and sixcarbon atoms. Those with six carbonatoms are known as the hexoses andhave the general formula C6H12O6.

Monosaccharides with an aldehydegroup (-CHO) are called aldoses.

Glucose has both an aldehyde groupand six carbon atoms and is thereforean aldohexose.

1 Chain structure For simplicity, monosaccharides are

sometimes displayed as vertical openchain structures to which the -H and–OH groups are attached.

Aldohexoses contain fourasymmetrical carbon atoms: C-2, C-3,C-4, and C-5. There are 8 differentpossible ways of arranging the –H and–OH groups on these carbon atoms,and each of these has two opticalisomers, making a total of 16.

The most important of these are thetwo optical isomers of glucose.

For glucose the D- and L- indicate theconfiguration of the –H and –OH

groups on C-5.

2 Ring structure In reality, solid monsaccharides do not

exist as open chain structures but asring structures.

In Howarth projections ofmonosaccharides, groups are shownon vertical bonds above and below aflat hexagonal ring.

D-glucose can exist in two separatecrystalline forms known and a-D-glucose and b-D-glucose. These formsare known as anomers.

3 Hexagonal ring The hexagonal ring in a

monosaccharide is not flat but in theform of a chair.

CHEMISTRY OF CARBON

174

cellulosedisaccharideglycogenmonosaccharide

polysaccharidestarchsucrose

Key words

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Disaccharides andpolysaccharides

glycosidic bond

CH2OH

OH O

O H

OH

HH

OHH

H

H

O

H

OHH

CH2OH

OH

H

OH

HH

OHH

H

H

O

H

OHH

CH2OH

OH H

OH

HH

OHH

CH2OH

OH H

OH

HH

OHH

CH2OH

OH H

OH

HH

OHH

CH2OH

OH

OH

HH

OHH

H

CH2OH

OH

O H

O

OH

CH2OH

O O O O

OHHOH

CH2OH

CH2OHH O

OH

HH

HO

HO

H O

HO H

CH2OH

H

2 Cellulose

3 Starch

1 Sucrose

Di-and polysaccharides A disaccharide is formed when two

monosaccharides join together. Amolecule of water is lost and aglycosidic link is formed.

A polysaccharide is a polymer formedby the joining of manymonosaccharide units.

1 Sucrose Sucrose, the sugar widely used on

foods, is a disaccharide.

2 Cellulose Cellulose, a polysaccharide, provides

plant cells with a rigid structure.

3 Starch Glycogen is the storage polysaccharide

of animals. Starch is the storage polysaccharide of

plants.

RADIOACTIVITY

Ionizing radiation Ionizing radiation is any radiation

capable of displacing electrons fromatoms or molecules and so producingions. Examples include alphaparticles, beta particles, and gammaradiation.

1 Alpha particles An alpha (a) particle has the same

structure as a helium nucleus (twoprotons and two neutrons).

Alpha particles are relatively heavy,high-energy particles with a positivecharge.

Alpha particles produce intenseionization in a gas.

Emission speeds are typically of theorder of 5–7 percent of the speed oflight.

2 Beta particles A beta (b) particle is a fast-moving

electron with a negative charge. Beta particles produce less ionization

in a gas than alpha particles and onaverage produce only 1/1000th asmany ions per unit length.

Emission speeds can be as high as 99percent of the speed of light.

3 Gamma radiation Gamma (g) rays ionize gas only weakly

and on average produce only 1/1000thas many ions per unit length as betaparticles.

4 Radiation in laboratories Sources of radiation used for

laboratory experiments are usuallysupplied mounted in a holder. Theactive material is sealed in metal foil,which is protected by a wire gauzecover. When not in use, the material isstored in a small lead container.

Ionizing radiationalpha particlebeta particlegamma radiationionizing radiation

Key words

175

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wire gauze cover

1 Alpha particles

α-radiation consistsof a stream of αparticles

Produces intenseionization in agas

proton

neutron

β-radiation consistsof a stream of βparticles

Produces lessintenseionization in agas than aparticles

2 Beta particles

electron

γ-radiation is a formof electromagneticradiation

Only weaklyionizes a gas

Wavelength <10–12 mFrequency >1021 Hz

4 mmplug

active metal foil

lead container

3 Gamma radiation

4 Radiation in laboratories

–

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Radiation detectorsRADIOACTIVITY

Detectors Radioactivity is invisible, but because

it affects the atoms that it passes,scientists can easily detect it using avariety of methods.

1 Spark counter High voltage is applied between the

stiff wire (anode) and the gauze(cathode) and reduced until it juststops sparking.

When a radium source is brought nearthe gauze, the air between the wireand the gauze is ionized, and sparksare seen and heard at irregularintervals.

2 Cloud chamber When air containing ethanol vapor is

cooled, it becomes saturated. Ifionizing radiation passes through thisair, further cooling causes the vapor tocondense on the ions created in theair. The result is a white line of tinyliquid droplets that shows up as atrack when illuminated.

3 GM tube When radiation enters the metal tube,

either through the mica window orthrough the tube wall, it creates argonions and electrons. These areaccelerated toward the electrodes andcollide with other argon atoms. Onreaching the electrodes, the ionsproduce a current pulse, which isamplified before being fed to a pulsecounter.

4 Testing absorption The ability of materials to absorb

alpha, beta, and gamma radiation canbe tested by placing the materialbetween a radioactive source and aGM tube and comparing the count perminute with the count over the sameperiod when the material is removed.

ionizing radiationradiationradioactivity

Key words

176

w

a aa a aaaaaaa aaaaaa

f

+

–

+

–

+–

––

–

––––

a stiff wire (anode)b sparksc wire gauze (cathode)d radium sourcee forcepsf insulating baseg E.h.t. supplyh circular transparent plastic

chamberi super-cooled vapor

j transparent lidk felt strip soaked with alcohol

and waterl basem radioactive sourcen foam spongeo crushed dry icep black metal base plateq mica windowr argon gas at low pressure

s anode wiret insulatoru cathode metal tubev pulse counterw electrons are pulled toward

the anode wire in an avalanche

x sourcey absorbing materialz GM tube

x

v

b

c

d

g

h j k

l

m

no

p

r s

u

tq

e

i

1 Spark counter 2 Cloud chamber

3 Geiger-Muller tube(GM tube)

4 Testing absorbtion ofalpha, beta, and gammaradiation

y z

RADIOACTIVITY

1 Penetration Alpha, beta, and gamma radiation

penetrate by different amounts. Alpha radiation is the least penetrating

and is stopped by a sheet of paper orvery thin metal foil.

Beta radiation is stopped by aluminuma few millimeters thick.

Gamma radiation is most penetrating,and is only stopped by a thick block oflead.

2 Range The penetrating power of alpha, beta,

and gamma radiation is reflected inthe distance that they can travelthrough air. Alpha particles can onlytravel a few centimeters beforecolliding with air particles. Betaparticles travels a few meters, whilegamma radiation can travel manymeters.

3 Gamma penetration Gamma rays are highly penetrating

because they have relatively littleinteraction with matter. There is verylittle absorption or scattering as theypass through air.

The intensity falls off with distanceaccording to the inverse square law:I = k

d2

where I is intensity, d is the distancefrom the source, and k is a constant.At a distance x, the intensity of thegamma radiation:Ix = k

x2

At a distance 2x, the intensity of thegamma radiation:I2x = k = k

(2x)2 4x2

As the distance increases by a factor of2, the intensity of the gamma radiationdecreases by a factor of 4.

alpha particlebeta particlegamma radiationradiation

Key words

177

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a

f

Cou

ntra

te

b

c

d

g

h

j

k

e

i

1 Penetration of radiation

1cm1cm3mm1mm

2 Range of radiation in air

1m 2m 3m

y

0 10 50 100 150 200 250 x1d2

3 The inverse square law for gamma radiation penetration

a α – sourceb β – sourcec γ – sourced metal foil

e paperf aluminumg lead

h α – a few centimetersi β – a few metersj γ – many metersk area covered by γ radiation at 1m distances

+

+

+

+

+

+

Properties of radiations:penetration and range

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RADIOACTIVITY

Electric and magneticfields An electric field is a field extending

outward in all directions from acharged particle.

A magnetic field is an area of force thatexists around a magnetic body or acurrent-carrying conductor. Alpha,beta, and gamma radiation behavedifferently in both.

1 Electric field Alpha radiation is composed of

positively charged particles. A streamof alpha particles is deflected whenpassing through the electric fieldbetween two oppositely chargedplates. The particles are repelled fromthe positively charged plate andattracted toward the negativelycharged plate.

Beta radiation is composed ofnegatively charged particles. A streamof beta particles is deflected by anelectric field in the opposite directionto alpha particles. The deflection isgreater because the beta particles havea much smaller mass.

Gamma radiation is not deflected byan electric field. This is evidence thatgamma radiation carries no charge.

2 Magnetic field Alpha radiation is deflected by a strong

magnetic field. Weak magnetic fieldshave no noticeable effect due to thegreater mass of alpha particlescompared to beta particles.

Beta radiation is deflected by arelatively weak magnetic field. Betaradiation is deflected in the oppositedirection to alpha radiation, indicatingits particles carry an opposite charge.

Gamma radiation is not deflected by amagnetic field, indicating that gammaradiation carries no charge.

alpha particlebeta particleelectric fieldgamma radiation

Key words

178

magnet

magnet

magnet

N

S

N

S

N

S

+

–

+

–

+

–

Radiation 1 Electric field 2 Magnetic field

Alpha

Beta

Gamma

Properties of radiations:in fields

RADIOACTIVITY

Stability The stability of isotopes is based on the

ratio of neutrons and protons in theirnucleus. Although most nuclei arestable, some are not andspontaneously decay, emittingradiation.

The lightest stable nuclides (particularisotopes of an element) have almostequal numbers of protons andneutrons. The heavier stable nuclidesrequire more neutrons than protons.The heaviest stable nuclides haveapproximately 50 percent moreneutrons than protons.

Odd-even rule Isotopes tend to be more stable when

they have even numbers of protonsand neutrons than when they haveodd. This is the result of the spins ofthe nucleons (the constituents of theatomic nucleus). When two protons orneutrons have paired spins (spins inopposite directions), their combinedenergy is less than when they areunpaired.

Decay When unstable nuclides disintegrate,

they tend to produce new nuclidesthat are nearer to the stability line.This will continue until a stablenuclide is formed.

An unstable nuclide above the band ofstability decays by beta emission. Thisincreases the proton number anddecreases the neutron number. Thus,the neutron to proton ratio isdecreased.

An unstable nuclide below the band ofstability disintegrates so as to decreasethe proton number and increase theneutron to proton ratio. In heavynuclides this can occur by alphaemission.

Stable and unstableisotopes

isotopenucleonnuclide

Key words

179

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Num

ber

ofne

utro

nsN

100

Number of protons (Z)

10 90

130

120

110

90

80

70

60

50

40

30

20

10

00 20 30 40 50 60 70 80

N = Z

Unstable region

Unstable region

band of stability

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Half-lifeRADIOACTIVITY

alpha particlehalf-lifeisotopenuclide

Key words

180

N0

N0

2

N0

4

1 Half-life

Num

ber

ofun

deca

yed

nucl

ei,N

Typical radioactive decay curve

Half-life

2 Rate of decay

Half-life Half-life Time, t

N0

N0

2

N0

4

N0

8

1 Half-life Half-life is the time required for half

the nuclei in a sample of an isotope toundergo radioactive decay.

Radioactive decay is a completelyrandom process in which nucleidisintegrate independently of eachother or external factors such astemperature and pressure.

2 Rate of decay There are always very large numbers of

active nuclides even in small amountsof radioactive material, so statisticalmethods can be employed to predictthe fraction that will have decayed, onaverage, over a given period of time.

The rate of decay of a nuclide at anytime is directly proportional to thenumber of nuclei, N, of the nuclide: -dN N or dN = -lN

dt dt

where N is the number of undecayednuclei and l is the decay constant. Theminus sign indicates that the numberof undecayed nuclei falls with time.Integrating this gives the exponentiallaw equation:Nt = N0e-lt

where N0 is the number of undecayedatoms at time t = 0 and Nt the numberof undecayed atoms after time t.

After one half life (t1/2) has passed, thenumber of undecayed atomsremaining in the sample will be N0/2.Substituting this into the exponentiallaw equation for Nt and taking naturallogs of both sides provides amathematical relationship between thedecay constant and the half life of aradioactive atom:t(1/2) = 0.693

l

RADIOACTIVITY

alpha particlehalf-lifeisotope

Key words

181

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Measuring half-life

1 Half-life of radon Thorium decays to produce the

radioactive isotope radon-220. Thisisotope is sometimes referred to asthoron.

The bottle containing thoriumhydroxide powder is squeezed a fewtimes to transfer some radon-220 tothe flask. The clips are then closed.

As the radon decays, the ionizationcurrent decreases. It is always ameasure of the number of alphaparticles present and, therefore, theproportion of radon-220 remaining.

The current is noted every 15 secondsfor 2 minutes and then every 60seconds for several minutes.

2 Exponential decay A graph of current against time is

plotted. In this experiment, the half-life is

indicated by the amount of time takenfor the current to fall to half of itsoriginal value.

The half-life of radon-220 isapproximately 55 seconds.

3 Radon decay Radon-220 decays with the loss of an

alpha particle to form polonium-216,which decays to form lead-212. Thehalf life of polonium-216 is 0.145seconds, and the half life of lead-212 is10.64 hours.

a

f

+

–

A

Time (s)

a ionization chamberb airc radond d.c. amplifiere clips

f valvesg squeezable polyethylene

bottleh thorium hydroxide powderi clock

b

c

d

g

h

e i

1 Half-life of radon

2 Exponential decay: decay curve for radon gas

Cur

rent

(am

ps)

0.125

0.25

0.5

1.0

00 50 100 150 200 x

y

Ra-222 Po-216 Pb-212

3 Radon decay

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Radioactive isotopesRADIOACTIVITY

1 Tracers Radioactive isotopes are used as tracers

to monitor the movement ofsubstances in plants and animals. Asolution containing radioactivephosphorus-32 is introduced into thestem of a plant. A Geiger counter isused to detect the movement of theisotope through the plant.

2 Thyroid monitor A solution containing iodine-131 is

introduced to the bloodstream of apatient with a defective thyroid. AGeiger counter is used to detect theisotope and monitor thyroid activity.

3 Food preservation Food is irradiated by exposing it to

gamma radiation. Irradiationdestroys disease-causing bacteria aswell as those that spoil food, so theshelf life of food is extended.

4 Sterilization Gamma radiation is used to sterilize

medical equipment.

5 Smoke detectors Americium-241, a source of alpha

radiation, is widely used in smokedetectors. The alpha particles ionizethe air in the sensing circuit. Anysmoke particles interfere with this andcause a change in the current, whichtriggers an alarm.

6 Duration of death All organisms contain a specific ratio of

radioactive carbon-14 to carbon-12.When an organism dies, no carbon-14is added. After death, carbon-14 decaysat a predictable rate: the half-life is5,700 years. By comparing the ratio ofcarbon-14 to carbon-12, it is possibleto say when an organism died.

alpha particlegamma radiationirradiationisotope

Key words

182

1 Tracers 2 Thyroid monitor

current-sensingcircuit

electriccurrent

gammarays

4 Sterilization

medical equipment

3 Food preservation

gammarays

bacteriadying

6 Duration of death5 Smoke detectors

Carbon-12constant

Carbon-14decreases

Deadorganism

Grasshopper

battery

RADIOACTIVITY

1 Nuclear fusion In nuclear fusion, two or more light

atomic nuclei join to make a moremassive one. During the process,some of the mass of the nuclei isconverted into energy. Nuclear fusion,which first occurred during the BigBang, powers stars. It also occurs inhydrogen bombs. Currently scientistsare working to control fusion so it canbe used in nuclear reactors.

2 Deuterium Deuterium is an isotope of hydrogen

known as heavy hydrogen. Thenucleus of a deuterium atom consistsof one neutron and one proton.

The fusion of two deuterium nucleiresults in the formation of a helium-3nucleus. A small amount of mass isconverted into energy:Mass of two deuterium nuclei = 2 x 2.014 = 4.028 u

Mass of helium-3 nucleus plus aneutron = 3.016 + 1.009 = 4.025 u

Mass converted to energy by fusion =4.028 – 4.025 = 0.003 u

Energy released by the fusion reaction= 4.5 x 10-13 J

Energy released per kilogram ofdeuterium is approximately 9 x 1013 J.

3 Tritium Tritium is another isotope of

hydrogen. The nucleus of a tritiumatom consists of two neutrons and oneproton.

The fusion of a deuterium nucleus anda tritium nucleus results in theformation of a helium-4 nucleus andthe release of energy. The energyreleased per kilogram of deuteriumand tritium is approximately 30 x 1013 J.

This reaction produces more energy,and the fusion takes place at a lowertemperature.

Nuclear fusionfusionisotope

Key words

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21 H 1

0 ndeuterium

2 Fusion of deuterium

21 H

deuterium

32 He

helium-3 neutron

21 H 1

0 ndeuterium

3 Fusion of deuterium and tritium

31 H

tritium

42 He

helium-4 neutron

1 Nuclear fusionproton

proton

positron

electron

positron

electron

starlight

proton

proton

heliumnucleus

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Nuclear fissionRADIOACTIVITY

Nuclear fission In nuclear fission, a heavy atomic

nucleus divides to make two smallerones. Some of the mass of the nuclei isconverted into energy during theprocess.

1 Reaction with uranium In a nuclear reaction with uranium and

slow-moving neutrons, the nucleus ofthe uranium-235 atom undergoesfission and forms two smaller nuclei(lanthanum-148 and bromine-85) plusthree neutrons. A small amount ofmass is converted to energy.

2 Chain reaction A nuclear chain reaction is a series of

self-sustaining reactions in which theparticles released by one nucleustrigger the fission of at least as manyother nuclei.

Under normal circumstances, only avery small proportion of fissionneutrons act in this way. However, ifthere is a sufficient amount of aradioactive isotope, a chain reactioncan start.

In an atomic bomb, an increasinguncontrolled chain reaction occurs ina very short time when two pieces ofuranium-235 (or plutonium-239) arerapidly brought together.

In a nuclear power station, the chainreaction is steady and controlled, soonly a limited number of fissionneutrons bring about further fissionreactions.

chain reactionfission

Key words

184

+ + +10 n 235

92U 14857La 85

35Br 310 n

1 Reaction with uranium

2 Chain reactionN

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

uranium-235 three neutrons

9 neutrons3 neutrons1 neutron

one neutron lanthanum-148 bromine-85

RADIOACTIVITY

Nuclear reactor Uranium, either the metal or the

metal oxide, is used as fuel in nuclearreactors. The fuel is in the form of fuelrods, which are suspended in thereactor.

Naturally occurring uranium contains99.3 percent uranium-238 and only 0.7percent of the radioactive isotopeuranium-235. The uranium-235content must be increased toapproximately 3 percent before theuranium can be use as a fuel.

Uranium-235 undergoes spontaneousfission. However, in a nuclear powerstation, the fission is brought about bybombarding the uranium nuclei withneutrons.

The fission of one atom of uranium-235 absorbs one neutron and releasesthree others. In order to increase thechances that these neutrons will strikeother uranium-235 atoms, they areslowed down by a moderator.

Control rods are suspended betweenthe fuel rods. These can be raised orlowered as needed to control thenuclear reaction. The control rods aremade of alloys that absorb neutrons.When they are lowered, moreneutrons are absorbed.

The heat produced by the fissionreaction is removed through a heatexchanger. The loop between thenuclear reactor and the heatexchanger is sealed so there is nodanger of radioactive material escapinginto the environment.

The heat is used to convert water intopressurized steam. The high pressuresteam drives a turbine connected to agenerator, which produces electricity.

Nuclear reactorfissionisotopeuranium

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concrete sheild cooling waterconverted to

steam, whichdrives turbine

cooling water

turbine

generator

electricity

cooling tower

atoms splitting insidecore of the reactor

give off heat

carbon dioxide gas carriesheat away from uranium inthe core of the reactor

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The uranium seriesRADIOACTIVITY

Radioactive decay Radioactive nuclei break down by a

process known as radioactive decayin order to become more stable. In aradioactive decay series, each memberof the series is formed by the decay ofthe nuclide before it until a stablenuclide is produced. As the nucleidisintegrate, they emit alpha (a) orbeta (b) particles.

There are three naturally occurringradioactive decay series: the uraniumseries, the actinium series, and thethorium series. Each ends with a stableisotope of lead.

The uranium series The uranium series involves the

radioactive decay of U-238 to stablePb-206. It is also known as the 4n+2

series (where n is an integer), becauseeach member of the series has a massequivalent to 4n+2.

The graph indicates how the decayoccurs. Atomic numbers are plottedon the x-axis. The mass numbers areon the y-axis. The symbol for theelement is at the top of the graph.Each diagonal line represents an alpha(a) decay; each horizontal line a beta(b) decay. A circle indicates thedaughter nucleus (the nucleusproduced by the decay of the previousnucleus). Half-life is indicated in years(a), days (d), hours (h), minutes (m),and seconds (s).

Decay chainU-238 Th-234 Pa-234 U-234 Th-230 Ra-226 Rn-222 Po-218 At-218 Pb-214 Bi-214 Po-214 Ti-210 Pb-210 Bi-210 Po-210 Pb-206 (stable)

186

α

β4.2m

138.3d5.0d

1.32m

22a 5.0d19.7m

1.6 × 10–4s26.8m

19.7m

3.05m 1.5s

3.05m

3.82d

1620a

8.0 × 104a

2.5 × 105a

24.1d

1.18m

4.5 × 109a

Mas

snu

mbe

r

230

89

Atomic number

225

210

205

20080 8887868584838281

220

235

Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U

90 91 92

215

240alpha particleatomic numberbeta particledaughter nucleushalf-life

mass numbernuclideradioactive decayuraniumuranium series

Key words

RADIOACTIVITY




The actinium series The actinium series involves the

radioactive decay of U-235 to stable Pb-207. It is also known as the 4n+3

series (where n is an integer), becauseeach member of the series has a massequivalent to 4n+3.


Decay chainU-235 Th-231 Pa-231 Ac-227 Th-227 Fr-223 Ra-223 Rn-219 Po-215 At-215 Pb-211 Bi-211 Po-211 Tl-207 Pb-207 (stable)

The actinium seriesactiniumactinium seriesalpha particleatomic numberbeta particle

daughter nucleushalf-lifemass numbernuclideradioactive decay

Key words

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α

β4.2m

0.52s2.16m

10–4s

3.92s

2.16m

21m

22.0a

3.43 × 104a

24.6h

7.1 × 108a

22.0a

18.6d

11.2d

1.83 × 10–3s

36.1m

Mas

snu

mbe

r

230

89

Atomic number

225

210

205

20080 8887868584838281

220

235


90 91 92

215

240

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The thorium seriesRADIOACTIVITY




The thorium series The thorium series involves the

radioactive decay of Th-232 to stablePb-208. It is also known as the (4n)series (where n is an integer) becauseeach member of the series has a massequivalent to 4n.


Decay chainTh-232 Ra-228 Ac-228 Th-228 Ra-224 Rn-220 Po-216 Pb-212 Bi-212 Po-212 Tl-208 Pb-208 (stable)

alpha particleatomic numberbeta particledaughter nucleushalf-life

mass numbernuclideradioactive decaythoriumthorium series

Key words

188

α

β

47m

10.6h

3.1m

54.5s

0.16s

6.7a

6.13h

1.39 × 1010a

1.90a

3.64d

3.0 × 10–7s

47m

Mas

snu

mbe

r

230

89

Atomic number

225

210

205

20080 8887868584838281

220

235


90 91 92

215

240

RADIOACTIVITY



The neptunium series is composed ofisotopes that do not occur in nature.

The neptunium series The neptunium series starts with the

artificial isotope plutonium-241 andends with bismuth-209. Each memberof the series has a mass equivalent to4n+1 (where n is an integer).

The graph indicates how the decayoccurs. Atomic numbers are plottedon the x-axis. The mass numbers areon the y-axis. The symbol of theelement is at the top of the graph.Each diagonal line represents an alpha(a) decay; each horizontal line a beta(b) decay. A circle indicates thedaughter nucleus (the nucleusproduced by the decay of the previousnucleus).

Decay chainPu-241 Am-241 Np-237 Pa-233 U-233 Th-229 Ra-225 Ac-225 Fr-221 At-217 Bi-213 Po-213 Pb-209 Bi-209 (stable)

The neptunium seriesalpha particleatomic numberbeta particledaughter nucleushalf-life

mass numberneptuniumneptunium seriesnuclideradioactive decay

Key words

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α

β

Mas

snu

mbe

r

230

89

Atomic number

225

210

205

20080 8887868584838281

220

235


90 91 92

215

245

240

Np Pu Am

Pu Am

NpU

UPa

Th

AcRa

Fr

At

Bi Po

BiPbTl

93 94 95

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Radioactivity of decaysequences

RADIOACTIVITY

1 Alpha decay Alpha decay is the process in which

the nucleus of an atom emits an alphaparticle (which has the same structureas the helium-4 nucleus: 4He).2

The new atom’s atomic mass number(A) is reduced by 4 and its atomicnumber (Z) is decreased by 2.

Uranium-238 decays to thorium-234 bythe loss of an alpha particle.

Energy is also released as gamma (g)radiation.

2 Alpha particle spectrum The ground state of the uranium

nucleus (the natural state of the lowestenergy of the nucleus) is at a higherenergy than the ground state of thethorium nucleus.

Some energy is released in the form ofkinetic energy, which is carried by thealpha particle.

The remaining energy is released asgamma radiation.

3 Beta decay Beta decay is the process in which the

nucleus of an atom emits a betaparticle (an electron).

The new atom’s atomic number (Z) isincreased by 1, while the atomic massnumber (A) remains unchanged.

Thorium-234 decays to protactinium-234 by the loss of a beta particle. Thehalf-life for this decay is 6.75 hours.

4 Beta particle spectrum The ground state of the thorium

nuclide is at a higher energy than theground state of the protractiniumnucleus.

Some energy is released in the form ofkinetic energy, which is carried by thebeta particle.

The remaining energy is released asgamma radiation.

alpha decayalpha particleatomic numberbeta decaybeta particle

gamma radiationground statekinetic energymass numbernuclide

Key words

190

a nuclide zb excited states of Z – 2c excited states of Z – 2d ground state of Z – 2

e alpha particle energyf gamma radiationg nuclide Zh excited state of Z + 1

i ground state of Z + 1j beta particle energyk neutrino energyl gamma radiation

1 Alpha decay

2 Alpha particle spectrum

3 Beta decay

4 Beta particle spectrum

General sequence of alpha decay

Example of alpha decay: uranium decay to thorium

X Y + HeaA A–4 4

Z Z–2 2+ g

U Th + Hea238 234 4

92 90 2+ g

a

b

c

d

g

h

jk

l

e

i

e

e ef

f

a a

g a a

g

General sequence of beta decay

X Y + e-bA A

Z Z+1+ n~

Th Pa + e-b234 A

90 91+ n~

Example of beta decay: thorium decay to protactinium

b

g

n~

b

g

b

n~

g

j

l l

j

k

RADIOACTIVITYTable of naturallyoccurring isotopes 1

atomic massatomic numberisotopemass number

Key words

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*denotes radioactive isotope

Table of masses and abundance of naturally occurring isotopes

Atomicmass

Element Symbol Massnumber(A)

Atomicnumber(Z)

Percentage

NeutronHydrogen

Helium

Lithium

BerylliumBoron

Carbon

Nitrogen

Oxygen

FluorineNeon

SodiumMagnesium

AluminumSilicon

PhosphorusSulfur

Chlorine

Argon

Potassium

Calcium

Scandium

nH

He

Li

BeB

C

N

O

FNe

NaMg

AlSi

PS

Cl

Ar

K

Ca

Sc

—99.990.011.3 × 10–11007.492.610019.680.498.91.199.60.499.760.040.2010090.90.38.810078.810.211.119992.24.73.110095.00.84.20.0175.524.50.340.0699.693.10.0126.997.00.60.12.10.0030.2100

1.0086651.0078252.0141023.0160304.0026046.0151267.0160059.01218610.01293911.00930512.00000013.00335414.00307415.00010815.99491516.99913317.99916018.99840519.99244020.99384921.99138422.98977323.98504524.98584025.98259126.98153527.97692728.97649129.97376130.97376331.97207432.97146033.96786435.96709134.96885436.96589535.96754837.96272430.96238438.96371439.96400849.96183539.96258941.95862842.95878043.95549045.95368947.95251944.955919

01

2

3

45

6

7

8

910

1112

1314

1516

17

18

19

20

21

1123467910111213141516171819202122232425262728293031323334363537363840*39404140424344464845

Atomic number The atomic number (Z) of an element

is the number of protons in thenucleus of one atom of that element.All atoms of the same element havethe same atomic number.

Element “Element” refers to the common name

of the element. This list is restricted tothe 89 naturally occurring elements.

Symbol “Symbol” refers to the shorthand form

of the element’s name used inchemical equations.

Mass number The mass number (A) represents the

number of protons or neutrons in thenucleus of one atom of that element.Not all atoms of the same elementhave the same mass number. Atoms ofan element that have different massnumbers are called isotopes.

Percentage “Percentage” refers to isotopic

abundance. For example, 99.99percent of naturally-occurringhydrogen has the mass number 1.Only 0.01 percent has the massnumber 2.

Atomic mass “Atomic mass” refers to the average

atomic mass of that element's isotopeweighted by isotopic abundance.

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192

Table of naturallyoccurring isotopes 2



Atomicmass


Atomicnumber(Z)

Percentage

Ti

V

Cr

MFe

CoNi

Cu

Zn

Ga

Ge

AsSe

Br

Kr

Titanium

Vanadium

Chromium

ManganeseIron

CobaltNickel

Copper

Zinc

Gallium

Germanium

ArsenicSelenium

Bromine

Krypton

4647484950*50515052535455545657585958606162646365646667687069717072737476757476777880827981788082838486

22

23

24

2526

2728

29

30

31

32

3334

35

36

8.07.374.05.55.20.2599.754.383.89.52.41005.891.72.20.310067.826.21.23.71.169.130.948.927.84.118.60.660.539.520.527.47.736.77.71000.99.07.623.549.89.250.649.40.32.311.611.556.917.4

45.95263346.9517647.94794848.94786749.94478949.94716550.94397849.94605151.94051452.94065153.93887954.93805453.9396255.9349356.9353957.9332758.93318957.9353459.9307860.9310561.9283463.9279662.9295964.9277963.92914565.9260566.9271567.9248669.9253568.9256870.9248469.9242871.9217472.923473.921175.921474.9215873.922475.9192376.9199377.9173579.9165181.916778.9183580.9163477.92036879.9163981.9134882.9141383.91150485.91062













RADIOACTIVITY


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Atomicmass


Atomicnumber(Z)

Percentage

72.127.90.69.97.082.510051.511.217.117.42.810015.99.115.716.59.423.89.6

5.61.912.712.617.131.618.51001.011.022.227.326.711.851.448.61.20.912.412.724.112.328.87.64.395.7

Rubidium

Strontium

YttriumZirconium

NiobiumMolybdenum

Technetium

Ruthenium

RhodiumPalladium

Silver

Cadmium

Indium

Rb

Sr

YZr

NbMo

Tc

Ru

RhPd

Ag

Cd

In

37

38

3940

4142

43

44

4546

47

48

49

8587*8486878889*909192949693929495969798100

969899100101102104103102104105106108110107109106108110111112113114116113115*

84.911786.909283.9133885.909386.908987.905688.905489.904390.905291.904693.906195.908292.906091.906393.904794.905795.904596.905797.905599.9076

95.907697.90598.9061

101.9037103.9055102.9048101.9049103.9036104.9046105.9032107.9039109.9045106.9050108.9047105.9059107.9040109.9030110.9041111.9028112.9046113.9036115.9050112.9043114.9041

has no stable or naturally-occuring isotopes













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Key words

194




Atomicmass


Atomicnumber(Z)

Percentage

Tin

Antimony

Tellurium

IodineXenon

CesiumBarium

Lanthanum

Cerium

Praseodymium

Sn

Sb

Te

IXe

CaBa

La

Ce

Pr

50

51

52

5354

5556

57

58

59

112114115116117118119120122124121123120122123124125126128130127124126128129130131132134136133130132134135136137138138*139136138140142*141

1.00.60.314.27.624.08.833.04.76.057.342.70.12.40.94.67.018.731.834.51000.10.11.926.44.121.226.910.48.91000.10.22.66.78.111.970.40.199.90.20.288.511.1100

111.9049113.9030114.9035115.9021116.9031117.9018118.9034119.9021121.9034123.9052120.9037122.9041119.9045121.9030122.9042123.9028124.9044125.90324127.9047129.9067126.90435123.9061125.90417127.90354128.90478129.90351130.90509131.90416133.90540135.90722132.9051129.90625131.9051133.9043134.9056135.9044136.9056137.9050137.9068138.9061135.9071137.9057139.90528141.9090140.90739













RADIOACTIVITY


Key words

195

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Atomicmass


Atomicnumber(Z)

Percentage

Neodymium

PromethiumSamarium

Europium

Gadolinium

TerbiumDysprosium

HolmiumErbium

ThuliumYtterbium

Lutetium

Nd

PmSm

Eu

Gd

TbDy

HoEr

TmYb

Lu

60

6162

63

64

6566

6768

6970

71

142143144*145146148150has no naturally occuring isotope144147*148149150152154151153152154155156157158160159156158160161162163164165162164166167168170169168170171172173174176175176*

27.312.323.88.317.15.75.5

3.115.111.314.07.526.622.447.852.20.22.215.120.615.724.521.71000.10.12.319.025.524.928.11000.11.633.422.927.114.91000.13.114.421.916.231.712.697.42.6

141.90748142.90962143.90990144.9122145.9127147.9165149.9207

143.9116146.91462146.9146148.9169149.9170151.9193153.9217150.9196152.9207151.9194153.9202154.9220155.9222156.9240157.9242159.9273158.924

159.924160.926161.926162.928163.928164.930

163.929165.929166.931167.931169.935

171.929

173.926

175.9414













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Key words

196




Atomicmass


Atomicnumber(Z)

Percentage

Hafnium

Tantalum

Tungsten

Rhenium

Osmium

Iridium

Platinum

GoldMercury

Thallium

Hf

Ta

W

Re

Os

Ir

Pt

AuHg

Tl

72

73

74

75

76

77

78

7980

81

174176177178179180180181180182183184186185187*184186187188189190*192*191193190192194195196198197196198199200201202204203205206*207*208*210*

175.9403176.9419177.9425178.9444179.9451179.9457180.9462179.9450181.9465182.9485183.9491185.951184.950186.9550

185.9529186.9550187.9550188.9572189.9574191.9605190.9599192.9623189.9592191.9605193.9624194.9645195.9646197.9675196.96655195.96582197.96677198.96826199.96834200.97031201.97063203.97348202.97233204.97446205.97608206.97745207.98201209.99000

0.25.218.627.113.735.20.0199.990.226.414.430.628.437.162.90.021.61.613.316.1

38.561.5

0.832.9

7.21000.110.016.923.113.229.86.929.570.5————













RADIOACTIVITY


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197

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Atomicmass


Atomicnumber(Z)

Percentage

Lead

Bismuth

Polonium

Astatine

Emanation

FranciumRadium

Actinium

Protactinium

Uranium

Pb

Bi

Po

At

Em

FrRa

Ac

Pa

U

82

83

84

85

86

8788

89

91

92

204206207208210*211*212*214*209210*211*212*214*210*211*212*214*215*216*218*215*218*219*220*222*223*223*224*226*228*227*228*230*231*232*234*231*234*234*235*238*

1.425.221.751.7————100—————————————————————————100———0.0060.71899.276

203.97307205.97446206.97590207.97664209.98418210.98880211.99190213.99976208.98042209.98411210.98729211.99127213.99863209.98287210.98665211.98886213.99519214.99947216.00192218.0089214.99866218.00855219.00952220.01140222.0175223.01980223.01857224.02022226.0254228.03123227.02781228.03117230.0331231.03635232.03821234.0436231.03594234.0434234.04090235.04393238.0508













KEY WORDS

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Key wordsaccelerator A chemical that increases the rate of a chemicalreaction.acid Any substance that releases hydrogen ions when addedto water. It has a pH of less than 7.acid-base indicator A chemical compound that changescolor when going from acidic to basic solutions. An exampleis Methyl orange.acidity The level of hydrogen ion concentration in asolution.actinides The name of the radioactive group of elementswith atomic numbers from 89 (actinium) to 103(lawrencium).actinium (Ac) A silvery radioactive metallic element thatoccurs naturally in pitchblende and can be synthesized bybombarding radium with neutrons.actinium series One of the naturally occurring radioactiveseries.activation energy The energy barrier to be overcome inorder for a reaction to occur. active site The part of an enzyme where the chemicalreaction occurs.addition polymerization A chemical reaction in whichsimple molecules are added to each other to form long-chainmolecules without by-products.addition reaction A reaction in which a molecule of asubstance reacts with another molecule to form a singlecompound. adsorption The process by which molecules of gases orliquids become attached to the surface of another substance. aerosol Extremely small liquid or solid particles suspendedin air or another gas.alcohol A member of a family of organic compounds whosestructure contains the –OH functional group. aldehyde One of a group of organic compounds containingthe aldehyde group (–CHO). Names have the suffix -al.aldohexose A monosaccharide having six carbon atoms andan aldehyde group.aldose A sugar containing one aldehyde group per moleculealkali A solution of a substance in water that has a pH ofmore than 7 and has an excess of hydroxide ions in thesolution.alkali metals Metallic elements found in group 1 of theperiodic table. They are very reactive, electropositive, andreact with water to form alkaline solutions.alkaline earth metals Metallic elements found in group 2of the periodic table. alkalinity Having a pH greater than 7.alkane A member of the hydrocarbon group whose generalformula is CnH2n+2. They have single bonds between thecarbon atoms and are not very reactive.alkanol See alcohol alkene A member of the hydrocarbon group whose generalformula is CnH2n. They have a double bond between a pair ofcarbon atoms and are thus reactive.alkyl A member of the hydrocarbon group whose generalformula is CnH2n+1.

alkyne A member of the hydrocarbon group with thegeneral formula CnH2n–1. They have a triple bond between a pair of carbon atoms in each molecule and are thusreactive.allotrope An element that can exist in more than onephysical form while in the same state. alloy A metallic material made of two or more metals or of ametal and non-metal. alpha decay The process of radioactive decay in which thenucleus of an atom emits an alpha particle.alpha particle A particle released during radioactive decaythat consists of two neutrons and two protons. aluminum (Al) A silvery-white. metallic element that isnon-magnetic and oxidizes easily.amine A member of a group of organic compoundscontaining the amino functional group –NH2.amino acid An organic compound containing both thecarboxyl group (–COOH) and the amino group (–NH2).ammonia (NH3) A colorless, strong-smelling poisonous gasthat is very soluble in water.ammonium hydroxide (NH4OH) An aqueous solutionof ammonia. It is a corrosive chemical with a strong odor.ammonium ion (NH4+) An ion found in ammoniasolution and in ammonium compounds. amphoteric Exhibiting properties of both an acid and a base.anhydride The substance remaining when one or moremolecules of water have been removed from an acid or abase. anhydrous Containing no water. Term applied to saltswithout water of crystallization.anion An ion having a negative charge.anode The electrode carrying the positive charge in asolution undergoing electrolysis.anomer A stereoisometric form of a sugar, involvingdifferent arrangements of atoms or molecules around acentral atom,aqueous solution A solution in which water is the solvent.argon Ar. A colorless, odorless. gaseous element. One of thenoble gases.aryl A member of an aromatic hydrocarbon group formed bythe removal of a hydrogen atom from an aromatichydrocarbon.association The process by which molecules of a substancecombine to form a larger structure. astatine At. A non-metallic radioactive element that is highlyunstable and rare in nature.atmosphere The layer of gases surrounding Earth.atom The smallest particle of an element that can exhibitthat element’s properties. atomic emission spectrum The amount ofelectromagnetic radiation an element emits when excited.atomic mass The ratio of the mass of an average atom ofan element to 1/12th of the mass of an atom of the carbon-12isotope. atomic number The number of protons in the nucleus ofan atom. atomic volume The volume of one mole of the atoms ofan element.Avogadro’s constant The number of particles present ina mole of substance.©

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azeotropic mixture A mixture of liquids that boils withouta change in composition.bakelite A phenol/methanal resin that has good electricaland heat insulation properties. base A substance existing as molecules or ions that can takeup hydrogen ions. beta decay The process of radioactive decay in which thenucleus of an atom emits a beta particle.beta particle A high-speed electron emitted by the nucleusof certain radioactive elements during beta decay. Big Bang The primeval explosion that most astronomersthink gave rise to the Universe.black hole An object with infinite density.body-centered cubic packing A crystalline structure inwhich one atom sits in the center of each cube.boiling point The point at which a substance changes fromthe liquid state to the gas state. bond The chemical connection between atoms within amolecule. Bonds are forces and are caused by electrons.bond angle In a molecule, the angle between the twostraight lines joining the centers of the atoms concerned.bromine (Br) A non-metallic element that is isolated as adark red liquid. It is a very reactive oxidizing agent. brown dwarf A ball of gas like a star but whose mass is toosmall to have nuclear fusion occur at its core.Brownian motion The random movement of particlesthrough a liquid or gas.buckminsterfullerene See buckyball.buckyball The nickname for buckminsterfullerene. Anallotropic form of carbon. It has a cage-like structure and hasthe formula C50, C60, or C70.burette A long, graduated glass tube with a tap at the lowerend. It is used to measure a volume of liquid accurately.calcium (Ca) A soft, slivery-white metal.calcium carbonate A white solid, occurring naturally inmarble and limestone, that dissolves in dilute acids.carbide A compound that contains carbon and an elementwith lower electronegativity. carbon (C) A non-metallic element whose compoundsoccur widely in nature.carbonate A salt of carbonic acid (containing the ionCO32–). carbon cycle The circulation of carbon through thebiosphere. carbon dioxide (CO2) A dense, colorless, odorless gasthat does not support combustion. It exists in theatmosphere and is instrumental in the carbon cycle. carbonic acid (H2CO3) A very weak acid formed bydissolving carbon dioxide in water.carbon monoxide(CO) A colorless, odorless, verypoisonous gas. It is sparingly soluble in water.carboxyl group The organic radical –CO.OH.carboxylic acid An organic acid that contains one or morecarboxyl groups.catalyst A substance that alters the rate of a chemicalreaction but remains chemically unchanged by it. catalytic cracking The process used in the petroleumindustry to convert large-chain hydrocarbon molecules tosmaller ones. catenation The formation of chains of bonded atoms.

cathode The electrode carrying the negative charge in asolution undergoing electrolysis.cathode rays A stream of electrons emitted from thecathode in a vacuum tube.cation An ion having a positive charge.cellulose A complex carbohydrate that is the maincomponent of the cell walls of plants.centrifuge A machine that rotates an object at high speed. chain reaction A self-sustaining nuclear reaction yieldingenergy and electrons emitted by the fission of an atomicnucleus, which proceeds to cause further fissions.chemical compound A substance composed of two ormore elements linked by chemical bonds that may be ionic orcovalent. chemical energy The energy stored in the bonds betweenatoms and molecules that is released during a chemicalreaction.chemical reaction The process in which one or moresubstances reacts to form new substances. chiral An object or a system that differs from its mirrorimage.chloride A compound containing chlorine and anotherelement. chlorine (Cl) A poisonous, greenish, gaseous element thatis a powerful oxidizing agent. chlorophyll A green pigment found in most plants. Itabsorbs light energy during photosynthesis.chromatography A technique for separating andidentifying mixtures of solutes in a solution. chromium (Cr) A hard, brittle, gray-white metallic elementthat is very resistant to corrosion and takes a high polish. cobalt (Co) A hard, lustrous, silvery-white metallic elementfound in ores, colloid A substance made of very small particles whose size(1–100 nm) is between those of a suspension and those insolution.compound See chemical compoundconcentration A measure of the quantity of solutedissolved in a solution at a given temperature. conductor A material that is able to conduct heat andelectricity.convection current A circular current in a fluid such as air. coordinate bonding A type of covalent bond in which oneof the atoms supplies both electrons.coordination number The number of atoms, ions, ormolecules to which bonds can be formed.copper (Cu) A pinkish metallic element used widely inalloys and electrical wires.covalent bond A bond formed when two electrons areshared between two atoms (usually between two non-metallicatoms), one contributed by each atom.covalent compound A compound in which the atoms inthe molecules are held together by covalent bonds. crust The outer layer of Earth.cryolite A compound of aluminum fluoride and sodiumfluoride. crystal A substance with an orderly arrangement of atoms,ions, or molecules in a regular geometrical shape.daughter nucleus In radio active decay, the nucleusproduced by the decay of the previous nucleus. ©

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dehydrating agent A substance that has an attraction forwater and is therefore used as a drying agent. dehydrogenation The chemical process of removal ofhydrogen atoms from a molecule (a form of oxidation),increasing its degree of unsaturation. density The mass per unit volume of a given substance.detergent The term for a synthetic soap substitute.diamond A transparent crystalline allotrope of carbon. It isthe hardest naturally occurring substance. diatomic molecule A molecule that consists of two atoms.diffusion The process of rapid random movement of theparticles of a liquid or gas that eventually form a uniformmixture.dipole A chemical compound with an unequally distributedelectric charge.disaccharide A sugar molecule formed by a condensationreaction between two monosaccharide molecules.displacement reaction A reaction in which a morereactive substance displaces the ions of a less reactivesubstance.dissociation The breaking down of a molecule into smallermolecules, atoms, or ions. dissolve To add a solute to a solvent to form a uniformsolution.distillation A process in which a solution is boiled and itsvapor then condensed. double bond A covalent bond formed between two atomsin which two pairs of electrons contribute to the bond..dry gas A gas from which all water has been removedductile Capable of being drawn out, shaped, or bent.effective collision A collision that brings about a reaction.electric field A field of force around a charged particle.electrode A conductor that allows current to flow throughan electrolyte, gas, vacuum, or semiconductor.electrolysis The process by which an electrolyte isdecomposed when a direct current is passed through itbetween electrodes. electrolyte A substance that forms ions when molten ordissolved in a solvent and that carries an electric currentduring electrolysis. electron One of the three basic subatomic particles. Verylight and carrying a negative charge, it orbits around thenucleus of an atom. element A substance that cannot be split into simplersubstances using chemical methods. emulsion A colloidal dispersion of small droplets of oneliquid dispersed within another, such as oil in water or waterin oil.enantiomer One of two “mirror images” of a chiralmolecule.end point The point at which a reaction is complete. endothermic a chemical change during which heat isabsorbed.enthalpy A measure of the stored heat energy of asubstance. enzyme An organic catalyst, made of proteins, that increasesthe rate of a specific biochemical reaction. equilibrium The state of a reversible chemical reactionwhere the forward and backward reactions take place at thesame rate.

equivalence point The point at which there are equivalentamounts of acid and alkali.ester A member of a hydrocarbon group that is formed by areaction between a carboxylic acid and an alcohol. ethane (C2H6) A colorless, flammable alkane that occurs innatural gas.ethanol (C2H5OH) A volatile, colorless liquid alcohol usedin beverages and as a gasoline octane enhancer.ethene (C2H4) A colorless, flammable unsaturated gas,manufactured by cracking petroleum gas, used in ethanol andpolyethene production.evaporation The change in state from liquid to vapor.exothermic A chemical change resulting in the liberation ofheat.face-centered cubic close packing A crystal structurein which one atom sits in each “face” of the cube.Faraday constant The amount of electricity needed toliberate one mole of a monovalent ion during electrolysis(9.648 670 x 10–4 C mol–1).fatty acid A hydrocarbon chain with a carboxyl group atone end. filtrate A clear liquid that has passed through a filter.filtration The process of removing particulate matter from a liquid by passing the liquid through a porous substance.fission A process during which a heavy atomic nucleusdisintegrates into two lighter atoms and the lost mass isconverted to energy.fluorescence The emission of light from an object that hasbeen irradiated by light or other radiations. fluorine (F) A gaseous non-metallic element that ispoisonous and very reactive gas.flux A substance that combines with another substance(usually an oxide), forming a compound with a lower meltingpoint than the oxide.foam A dispersion of gas in a liquid or solid. Small bubblesof gas are separated by thin films of the liquid or solid.formula mass The relative molecular mass of a compoundcalculated using its molecular formula. The mass of a mole ofthe substance.forward reaction A reaction in which reactants areconverted to products.fractional distillation The separation of a mixture orliquids that have differing but similar boiling points. fullerenes Allotropes of carbon in the form of a hollowsphere (buckyball) or tube (nanotube).functional group The atom (or group of atoms) present ina molecule that determines the characteristic properties ofthat molecule.fusion The process by which two or more light atomicnuclei join, forming a single heavier nucleus. The products offusion are lighter than the components. The mass lost isliberated as energy.galvanizing The coating of iron or steel plates with a layerof zinc to protect against rusting. gamma radiation Very short-wave electromagneticradiation emitted as a result of radioactive decay. gas One of the states of matter. In a gas, the particles canmove freely throughout the space in which it is contained.Gas is the least dense of the states of matter.©

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gas-liquid chromatography A type of chromatographyin which the mobile phase is a carrier gas and the stationaryphase is a microscopic layer of liquid on an inert solidsupport.gel A colloidal solution that has formed a jelly. The solidparticles are arranged as a fine network in the liquid phase.geometric isomerism A form of isomerism that describesthe orientation of functional groups at the ends of a bondwhere no rotation is possible.glucose In animals and plants, the most widely distributedhexose sugar and the most common energy source inrespiration. glycogen A polysaccharide composed of branched chains ofglucose, used to store energy in animals and some fungi..gold (Au) A shiny, yellow metallic element used in coins,jewelry, and electrical contacts.grade The concentration of ore in rock.Graham’s law The velocity with which a gas will diffuse isinversely proportional to the square root of its density.graphite A soft, grayish-black, solid allotrope of carbon. ground state The lowest allowed energy state of an atom,molecule, or ion. group The vertical columns of elements in the periodictable. Elements in a group react in a similar way and havesimilar physical properties. group 1 elements The alkali metals. The elements lithium,sodium, potassium, rubidium, cesium, and francium. Theseelements have one electron in their outer shell. group 2 elements The alkaline earth metals. Theelements beryllium, magnesium, calcium, strontium, barium,and radium. These elements have two electrons in their outershell. group 3 elements The elements boron, aluminum,gallium, indium, and thallium. These elements have a full sorbital and one electron in a p orbital in their outer shell. group 4 elements The elements carbon, silicon,germanium, tin, and lead. These elements have a full s orbitaland two electrons in two p orbitals in their outer shell. group 5 elements The elements nitrogen, phosphorus,arsenic, antimony, and bismuth. These elements have a full sorbital and three electrons in three p orbitals in their outershell. group 6 elements The chalcogens. The elements oxygen,sulfur, selenium, tellurium, and polonium. These elementshave a full s orbital, one full p orbital, and two half-full porbitals in their outer shell. group 7 elements The halogens. The elements fluorine,chlorine, bromine, iodine, and astatine. These elements havea full s orbital, two full p orbitals, and one half-full p orbital intheir outer shell. group 8 elements. The noble or inert gases. The elementshelium, neon, argon, krypton, xenon, and radon. The outershell of the atoms in these elements is complete, renderingthese elements unreactive. half-life The time required for half the atoms of aradioactive substance to disintegrate. halide A compound that a halogen makes with anotherelement. Metal halides are ionic; non-metal halides areformed by covalent bonding.halogens See Group 7 elements.

helium (He) A colorless, odorless gaseous element that isthe second most abundant element on Earth.hexagonal close packing In crystalline structures, a wayof packing atoms so that alternating layers overlie oneanother in an ABABAB pattern.hexose A monosaccharide with six carbon atoms.homologous series A series of related organiccompounds. The formula of each member differs from thepreceding member by the addition of a –CH2– group. hydration The combination of water and another substanceto produce a single product.hydride A compound formed between hydrogen andanother element. hydrocarbon An organic molecule consisting only ofcarbon and hydrogen.hydrochloric acid (HCl) A colorless fuming solution ofhydrogen chloride. hydrogen (H) An odorless, easily flammable gaseouselement that is the most abundant on Earth.hydrogen bond A weak bond between hydrogen andanother element with partial but opposite electrical charges. hydrogen chloride (HCl) A colorless gas with a pungentsmell that fumes in moist air. It is very soluble in water.hydrogen peroxide (H2O2) A colorless or pale blueviscous liquid. It is a strong oxidizing agent, but it can also actas a reducing agent. hydrogen sulfide (H2S) A colorless, poisonous gassmelling of bad eggs that is moderately soluble in water. It isa reducing agent.hydronium ion The positive ion (H3O)+. It is the hydratedform of the hydrogen ion (H+) or proton.hydrophilic Water-loving. In solution, it refers to a chemicalor part of a chemical that is highly attracted to water.hydrophobic Water-hating. It refers to a chemical or part ofa chemical that repels water.hydroxide A compound containing the hydroxide ion or thehydroxyl group bonded to a metal atom. hydroxide ion The negative ion (OH–) present in alkalis. immiscible Incapable of mixing.indicator A substance that indicates by a change in its colorthe degree of acidity or alkalinity of a solution or thepresence of a given substance. inert A substance that is either very or completelyunreactive. inert gases See noble gases.infrared Electromagnetic radiation with a greaterwavelength than the red end of the visible spectrum.insoluble A substance that does not dissolve in a particularsolvent under certain conditions of temperature andpressure.iodine (I) A grayish-black non-metallic element that isessential in the diet and is used in disinfectants andphotography.ion An electrically charged atom or group of atoms. ionic bonding A type of bonding that occurs when atomsform ions and electrons are transferred from one atom toanother.ionic compound Compounds consisting of ions heldtogether by strong ionic bonds. Ionic compounds areelectrolytes. ©

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ionic crystal A type of crystal where ions of two of moreelements form a regular three-dimensional arrangement(crystal structure). ionization energy The energy needed to removecompletely an electron from a neutral gaseous atom or ionagainst the attraction of the nucleus. ionizing radiation Any radiation capable of displacingelectrons from atoms or molecules and so producing ionsiron (Fe) A silvery, malleable and ductile metallic elementused in construction.irradiation The use of radiation to destroy microorganismsin foods.isomer One of two or more (usually organic) compoundshaving the same molecular formula and relative molecularmass but different three-dimensional structures. isomerism The rearrangement atoms in a molecule tomake it more efficient.isomerization The transformation of a molecule into adifferent isomer.isotope Atoms of the same element (all chemically identical)having the same atomic number but containing differentnumbers of neutrons, giving a different mass number.ketone An organic compound that contain two organicradicals connected to a carbonyl group. kinetic energy The energy a body has by virtue of itsmotion.lanthanide series A series of metallic elements with theatomic numbers 57 to 71. The metals are shiny and areattacked by water and acids.lattice The orderly three-dimensional arrangements ofatoms, molecules, or ions seen in crystals.lead (Pb) A silvery-white metallic element used in batteriesand in water, noise, and radiation shielding. lead sulfide (PbS) A brownish-black insoluble crystal. Itoccurs naturally as the mineral galena.Le Chatelier’s principle If a chemical reaction is atequilibrium and a change is made to any of the conditions,further reaction will take place to counteract the changes inorder to re-establish equilibrium.limewater A solution of calcium hydroxide that is used totest for the presence of carbon dioxide. limiting form The possibilities for the distribution ofelectrons in a molecule or ion.liquid A state of matter between solid and gas. Particles areloosely bonded, so can move relatively freely. lone pair A pair of electrons in the outermost shell of anatom that are not involved in the formation of covalentbonds.luminescence Light emission from a substance caused byan effect other than heat. magnesium (Mg) A silvery-white metallic element used inalloys and castings. magnesium oxide (MgO) A white solid used forreflective coatings and as a component of semiconductors.manganese (Mn) A soft, gray metallic element used inmaking steel alloys.mantle The layer of Earth between the crust and the core.mass The measure of a body’s resistance to acceleration.mass number The total number of protons and neutronsin the nucleus of an atom.

mass spectrometry A technique for determining thecomposition of molecules by using the mass of their basicconstituentsmelting point The point at which a substance changesstate from solid to liquid. methane (CH4) The simplest alkane. A colorless, tasteless,odorless flammable gas used as a fuel. mineral A natural inorganic substance with distinct chemicalcomposition and internal structure.mixture A system consisting of two or more substances thatare not chemically combined.mobile phase The phase that moves along the stationaryphase. It is the solvent in paper chromatography.molarity The concentration of solution giving the numberof moles of solute dissolved in 1 kg of solvent.mole The amount of a substance that contains the samenumber of entities (atoms, molecules, ions, etc.) as there areatoms in 12 g of the carbon-12 isotope. molecular mass The sum of the atomic masses of allatoms in a molecule. The mass of a mole of the substance.molecule The smallest part of an element or chemicalcompound that can exist independently with all theproperties of the element or compound. monomer A basic unit from which a polymer is made.monosaccharide A simple sugar such as glucose.nanotube An isotope of carbon consisting of long thincylinders closed at either end with caps containingpentagonal rings. neptunium (Np) A radioactive metallic element that can besynthesized by bombarding U-238 with neutrons.neptunium series A radioactive series composed ofartificial isotopes.neutral A solution whose pH is 7.neutralization The reaction of an acid and a base forming asalt and water..neutron One of the two major components of the atomicnucleus. It has no electric charge.neutron star The smallest but densest kind of star,apparently resulting from a supernova explosion.nickel (Ni) A hard, malleable and ductile, silvery-whitemetallic element that is a component of Earth’s core. nitrate A salt of nitric acid. nitric acid (HNO3) A colorless, corrosive, poisonous,fuming liquid that is a strong oxidizing agent. nitrite A salt of nitrous acid. nitrogen (N) A colorless gaseous element essential for thegrowth of plants and animals.nitrogen cycle The process by which nitrogen is recycledin the ecosystem. noble gases Group 8 elements: helium, neon, argon,krypton, xenon, and radon. These gases do not combinechemically with other materials. nucleon A proton or neutron.nucleus The positively charged core of an atom thatcontains almost all its mass. nuclide A particular isotope of an element, identified by thenumber of protons and neutrons in the nucleus.optical isomerism A form of isomerism in which twoisomers are the same in every way except that they are mirrorimages that cannot be superimposed on each other.©

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orbital An area around an atom or molecule where there is ahigh probability of finding an electron. ore A mineral from which a metal or non-metal may beprofitably extracted.oxidation The process by which a substance gains oxygen,loses hydrogen, or loses electrons.oxidation state The sum of negative and positive chargesin an atom. oxide A compound consisting only of oxygen and anotherelement. Oxides can be either ionic or covalent.oxidizing agent A substance that can cause the oxidationof another substance by being reduced itself.oxygen (O) A colorless, odorless gaseous element. It themost common element in Earth’s crust and is the basis forrespiration in plants and animals..ozone (O3) One of the two allotropes of oxygen. A bluishgas with a penetrating smell, it is a strong oxidizing agent.period The horizontal rows of elements in the periodictable. periodic table A table of elements, arranged in ascendingorder of atomic number, that summarizes the majorproperties of the elements.periodicity Recurring at regular intervals.peroxide A compound that contains the peroxide ion O22–.Peroxides are strong oxidizing agents. pH A scale from 0 to 14 that measures the acidity or alkalinityof a solution. A neutral solution has a pH of 7, while an acidicsolution has a lower value and an alkaline solution a highervalue.pH meter A device that uses an electrochemical cell tomeasure pH.phosphorescence The emission of light by an object, andthe persistence of this emission over long periods, followingirradiation by light or other forms of radiation. photochemical reaction A chemical reaction that isinitiated by a particular wavelength of light.photoelectric effect The emission of electrons frommetals upon the absorption of electromagnetic radiation.photosynthesis The photochemical reaction by whichgreen plants make carbohydrates using carbon dioxide andwater. platinum (Pt) A soft, shiny, silver metallic transitionelement that is malleable and ductile. pollutant A substance that harms the environment when itmixes with air, soil, or water.polyethene A thermoplastic polymer made by additionpolymerization of ethene. polymer A material containing very large molecules built upfrom a series of repeated small basic units (monomers). polymerization The building up of long chainhydrocarbons from smaller ones.polysaccharide A organic polymer composed of manysimple sugars (monosaccharides).precipitate An insoluble substance formed by a chemicalreaction. product A substance produced during a chemical reaction. protein A large, complex molecule composed of a longchain of amino acids.proton The positively charged particle found in the nucleusof the atom.

protostar The early stage in a star’s formation before theonset of nuclear burning.quantum number The number used when describing theenergy levels available to atoms and molecules. racemate A mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule.radiation Energy that is transmitted in the form of particles,rays, or waves.radical A group of atoms forming part of many molecules. radioactive decay The process by which unstableradioactive atoms are transformed into stable, non-radioactiveatoms. radioactivity The spontaneous disintegration of certainisotopes accompanied by the emission of radiation.rate of reaction The speed at which a chemical reactionproceeds.reactant A substance present at the start of a chemicalreaction that takes part in the reaction. reaction A process in which substances react to form newsubstances. reactivity The ability of substances to react to form newsubstances. reactivity series of metals Metallic elements arrangedin order of their decreasing chemical reactivity. reagent A substance that takes part in a chemical reaction,one that is usually used to bring about a chemical change.red giant A very large, cool star in the final stages of its life.redox reaction A process in which one substance isreduced and another is oxidized at the same time.reducing agent A chemical that can reduce another whilebeing oxidized itself.reduction A chemical reaction in which a substance gainselectrons, looses oxygen, or gains hydrogen. It is the reverseof oxidation.reforming The conversion of straight chain molecules intothose that are branched in order to improve their efficiencies.residfining The process used on the residue fraction ofcrude oil to convert it into a usable product. residue The solid remaining after the completion of achemical process.resonance structure In organic chemistry, a diagrammatictool to symbolize bonds between atoms in molecules.respiration The chemical reaction by which an organismderives energy from food.reverse reaction A reaction in which the products areconverted into reactants.reversible reaction A chemical reaction that can proceedin either direction. It does not reach completion but achievesdynamic equilibrium.Rf value The ratio of the distance moved by a substance in achromatographic separation to the distance moved by thesolvent.rust A reddish-brown oxide coating on iron or steel causedby the action of oxygen and water.salt A compound formed from an acid in which all or part ofthe hydrogen atoms are replaced by a metal or metal-likegroup. Salts are generally crystalline.saponification The treatment of an ester (hydrolysis) witha strong alkaline solution to form a salt of a carboxylic acidand an alcohol. ©

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saturated A solution where there is an equilibrium betweenthe solution and its solute.scandium (Sc) Silvery-white metallic element in thelanthanide series found in nature only in minute quantities.sewage Wastewater from domestic and industrial sources.shell A group of orbitals at a similar distance from an atomicnucleus.silver (Ag) A white, shiny, ductile metallic element. silver nitrate (AgNO3) A very soluble white salt thatdecomposes to form silver, oxygen, and nitrogen dioxide onheating. slag Waste material that collects on the surface of a moltenmetal during the process of either extraction or refining. smelting The process of extracting a metal from its ores. soap A cleansing agent made from fatty acids derived fromnatural oils and fats.sodium (Na) A soft, silver-white metallic element. sodium chloride (NaCl) A nonvolatile ionic compoundthat is soluble in water. sodium hydroxide (NaOH) A white, translucent,crystalline solid that forms a strongly alkaline solution inwater. sol A liquid solution or suspension of a colloid.solid A state of matter in which the particles are not free to move but in which they can vibrate about fixed positions. solubility A measure of the quantity of a solute that willdissolve in a certain amount of solvent to form a saturatedsolution under certain conditions of temperature andpressure. solubility curve A graphic representation of the changingsolubility of a solute in a solvent at different temperatures.soluble A relative term that describes a substance that candissolve in a particular solvent. solute A substance that dissolves in a solvent and thus formsa solution.solution A uniform mixture of one or more solutes in asolvent. solvent A substance, usually a liquid, in which a solutedissolves to form a solution.species The common name for entities (atoms, molecules,molecular fragments, and ions) being subjected toinvestigation.spectrum The arrangement of electromagnetic radiationinto its constituent wavelengths.starch A polysaccharide with the formula (C6H10O5). It iscomposed of many molecules of glucose.stationary phase That which the mobile phase moves on.In paper chromatography it is the paper.stoichiometry The calculation of the quantities of reactantsand products involved in a chemical reaction. subatomic particles The particles from which atoms aremade. Neutrons and protons are found in the nucleus of theatom. Electrons form a cloud around the nucleus.sucrose A disaccharide sugar that occurs naturally in mostplants.sulfate A salt or ester of sulfuric acid.

sulfide A compound of sulfur and a more electropositiveelement.sulfur (S) A yellow, non-metallic element that is foundabundantly in nature. sulfuric acid (H2SO4) An oily, colorless, odorless liquidthat is extremely corrosive. sulfur dioxide (SO2) A colorless gas with a pungent odorof burning sulfur. It is very soluble in water. sulfur trioxide (SO3) A white, soluble solid that fumes inmoist air. It reacts violently with water to form sulfuric acid. supernova The explosion caused when a massive star diesand collapses.surface area The sum of the area of the faces of a solid.suspension A type of dispersion. Small solid particles aredispersed in a liquid or gas.tensile strength The amount of stress a material can standwithout breaking.thorium Th. A gray, radioactive metallic element used as fuelin nuclear reactors.thorium series One of the naturally occurring radioactiveseries.titanium (Ti) A lightweight, gray metallic element that isvery strong and resistant to corrosion.titration In analytical chemistry, A technique used todetermine the concentration of a solute in a solution.transition metals Metallic elements that have anincomplete inner electron structure and exhibit variablevalencies. triple bond A covalent bond formed between two atoms inwhich three pairs of electrons contribute to the bond.ultraviolet Electromagnetic radiation of shorterwavelengths than visible light, but of longer wavelength thanX rays.unit cell The smallest repeating array of atoms, ions, ormolecules in a crystal.universal indicator A mixture of substances that shows agradual color change over a wide range of pH values. uranium (U) A hard, white, radioactive metallic elementused in nuclear reactors and nuclear weapons.uranium series One of the naturally occurring radioactiveseries.valency The measure of an element’s ability to combinewith other elements.vanadium (V) A silvery-white or gray metallic element usedas a steel additive and in catalysts.van der Waals forces Weak intermolecular or interatomicforces between neutral molecules or atoms. They are muchweaker than chemical bonds.viscosity A measure of the resistance of a fluid to flow.wavelength The distance between two correspondingpoints on a wave.white dwarf The small, dense remnant of a star near theend of its period of nuclear fusion.zinc (Zn) A hard, brittle, bluish-white metallic element usedin alloys and in galvanizing.zwitterion An ion that carries both a positive and negativecharge.

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INTERNET RESOURCES

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Internet resourcesThere is a lot of useful information on the internet.Information on a particular topic may be availablethrough a search engine such as Google(http://www.google.com). Some of the Web sites that arefound in this way may be very useful, others not. Belowis a selection of Web sites related to the materialcovered by this book.

The publisher takes no responsibility for theinformation contained within these Web sites. All the sites were accessible on March 1, 2006.

About ChemistryIncludes links to a glossary, encyclopedia, experiments,periodic table, chemical structure archive, chemistryproblems, and articles.

http://chemistry.about.com

Allchemicals.infoHundreds of definitions and descriptions from absolutezero to zinc.

http://www.allchemicals.info

Chem4KidsAccessible information on matter, atoms, elements,reactions, biochemistry, and much more, for grades 5–9.

http://www.chem4kids.com

Chemistry Carousel: A Trip Around the CarbonCycleSite explaining the carbon cycle.

http://library.thinkquest.org/11226

Chemistry CentralOffers basic atomic information, information on theperiodic table, chemical bonding, and organic chemistryas well as extensive links to a wide variety of otherresources.

http://users.senet.com.au/~rowanb/chem

Chemistry.orgOffers publications, career advice, information, andcurriculum materials for K–12.

http://www.acs.org/

The Chemistry Research CenterOffers high school students links to useful sites for helpwith homework.


Chemistry TutorHelp for high school students with chemistry homework.Includes an introduction to chemistry, equations,calculations, types of reactions, information on lab safety,and links to other sources.


ChemSpy.comLinks to chemistry and chemical engineering terms,definitions, synonyms, acronyms, and abbreviations.

http://www.chemspy.com

ChemtutorA guide to the basics of chemistry for high school andcollege students.

http://www.chemtutor.com

CHEMysteryA virtual chemistry textbook, providing an interactiveguide for high school chemistry students and links toother resources.


Common MoleculesInformation and 3-D presentation on molecules studiedin chemistry classes or of interest for their structuralproperties.

http://www.reciprocalnet.org/edumodules/commonmolecules

Delights of ChemistryPresents more than 40 chemistry demonstrations and500 photographs/animations of experiments andchemical reactions.

http://www.chem.leeds.ac.uk/delights

EnvironmentalChemistry.comIncludes a chemical and environmental dictionary; adetailed periodic table of elements; articles onenvironmental and hazardous materials issues; a geologictimeline.

http://environmentalchemistry.com

Eric Weisstein’s World of CHEMISTRYOnline encyclopedia, still under construction, withexcellent graphics; good source for chemical reactions.

http://scienceworld.wolfram.com/chemistry

General Chemistry OnlineContains searchable glossary, frequently askedquestions, database of compounds, tutorials,simulations, and toolbox of periodic table andcalculators.

http://antoine.frostburg.edu/chem/senese/101 ©D

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IUPAC Nomenclature Home PageDefinitions of terms used in chemistry provided by theInternational Union of Pure and Applied Chemistry. The“Gold book” is particularly good for basic terms.

http://www.chem.qmul.ac.uk/iupac

The Learning Matters of ChemistryOffers visualizations of molecules and atomic orbits,interactive chemistry exercises, and links to otherresources.

http://www.knowledgebydesign.com/tlmc

The Macrogalleria: A Cyberwonderland ofPolymer FunAn Internet “mall” for learning about polymers andpolymer science.

http://www.pslc.ws/macrog

Nuclear Chemistry and the CommunityIntroduction to nuclear chemistry and its impact onsociety.

http://www.chemcases.com/nuclear

Open Directory Project: Biochemistry andMolecular BiologyA comprehensive listing of internet resources in thefield of biochemistry.

http://dmoz.org/Science/Biology/Biochemistry_and_Molecular_Biology

Open Directory Project: ChemistryA comprehensive listing of internet resources in thefield of chemistry.

http://dmoz.org/science/chemistry

The pH FactorIntroduction to acids and bases for middle schoolstudents.

http://www.miamisci.org/ph

PSIgate: ChemistryOffers interactive tutorials, timeline, and links, in manyareas.

http://www.psigate.ac.uk/newsite/chemistry-gateway

Reactive ReportsWeb chemistry magazine offering news stories and linksto sites.

http://www.reactivereports.com

ScienceMasterNews, information, links, columns, and homework helpin all major areas of science.

http://www.sciencemaster.com

Science News for KidsScience Service Suggestions for hands-on activities,books, articles, Web resources, and other useful materials for students ages 9–13.

http://www.sciencenewsforkids.org

The Science of SpectroscopyIntroduction to spectroscopy with descriptions ofcommon spectroscopic analysis techniques, as well asapplications of spectroscopy in consumer products,medicine, and space science.

http://www.scienceofspectroscopy.info

Virtual Chemistry3-D simulated laboratory for teaching chemistry, withlinks to an online encyclopedia, tutorials, and close-upsof molecules.

http://neon.chem.ox.ac.uk/vrchemistry

A Visual Interpretation of the Table of ElementsStriking visual representations of 110 elements. Siteincludes detailed information on the elements and onthe history of the periodic table.

http://www.chemsoc.org/viselements

Web Elements™ Periodic Table Scholar EditionHigh quality source of information about the periodictable for students. There is also a professional edition.

http://www.webelements.com/webelements/scholar

What’s that Stuff?Explores the chemistry of everyday objects.

http://pubs.acs.org/cen/whatstuff/stuff.html

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INDEX

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IndexIndex of subject headings.

acidsneutralization of 130preparation of 124reactions of 123, 170titration of 53–4

actinium series 187air, gases in 69alcohols 163, 170alkalis, neutralization of 127alkanes 156

reaction summary 169alkenes 157

reaction summary 169allotropes

of carbon 148–9of oxygen 82of sulfur 82

aluminum 106reactions of 112

amino acids 172ammonia 67, 73–7

Haber process 74–5properties of 73

atomic emission spectrum 22atomic mass 35atomic structure 13atomic volumes 33–4Avogadro’s constant 20

bases 125–6neutralization of 128

boiling points 31–2bond dissociation energies 140bonding of chemicals 41–4

carbon, chemistry of 148–74carbon chains 154carbon cycle 150carbon oxides 151carboxylic acids 164

catalysts 141–2cathode ray oscilloscopes 17changes in matter 45–63chemical combination 41–4chemical reactions 119–47chlorine, compounds of 93chromatography 49–50collision theory 131colloids 46compounds, molecular, masses of

37contact process 85–6coordinate bonding 44copper

reactions of 111–12smelting and conversion of 110

copper sulfate, solubility of 63covalent bonding 43crude oil, fractional distillation of

152crystal structure of metals 39–40crystals, ionic 38

decay sequencesactinium series 187neptunium series 189radioactivity of 190thorium series 188uranium series 186

detergents 166diamonds 148disaccharides 174distillation, simple and fractional

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efficient packing 40electrode activity and

concentration 122electrolysis 121–2electron structure of metals 104electrons 15–18elements

atomic volumes of 33boiling points of 31first ionization energies of 27melting points of 29organization of 25periodic table 26, 36

endothermic reactions 139energy levels 23esters 165ethene 158exothermic reactions 139

fertilizers, nitrate 79first ionization energy 27–8fission, nuclear 184flame tests on metals 115fractional distillation 47

of crude oil 152fullerenes 149functional groups 162

gas-liquid chromatography 50gases in air 69Geiger and Marsden’s apparatus

14graphite 148

Haber process 74–5half-life 180–1halogens 91–2, 95–7homologous series 162hydrocarbons, naming of 155hydrogen 22–3, 64–8hydrogen chloride 94

ionic bonding 41ionic crystals, structure of 38ionic radicals 42ionic salts 59ionic solutions 60ionization energies of transition

metals 105ionizing radiation 175iron

smelting of 107reactions of 112

isotopesnaturally occurring 191–7radioactive 182stable and unstable 179

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lattice structure of metals 39luminescence 24

massatomic 35molecular 37

mass spectrometry 50melting points 29–30metal hydroxides 116metal ions 117metallic carbonates 129metals

crystal structure of 39–40electron structure of 104extraction of 113group 1 and group 2 100–3ores of 99reactivity of 114, 119–20tests on 115–17uses of 118world distribution of 98

mixtures 45molecular mass 37mole, the 21molecules, size and motion of 19monosaccharides 173

naturally occurring isotopes191–7

neptunium series 189neutralization of alkalis, bases and

acids 127–30nitrate fertilizers 79nitric acid 76–7nitrogen 70–1, 77–8nitrogen cycle 72nuclear power 183–5

optical isomerism 171ores of metals 99, 113organic compounds 167oscilloscopes 17oxidation and oxidation states

88, 143, 147oxides of sulfur 84oxygen 80–3, 88–9

paper chromatography 49periodic table 26, 36pH scale 51, 55planets

composition of 11density, size, and atmosphere of12

polymers 159–61polysaccharides 174proteins 172proton transfer 127–30

radiationsdetection of 176properties of 177–8

radioactivity 175–97of decay sequences 190

reaction rates 132–8reactivity of metals 119–20redox reactions 144–6

of halogens 96reduction of oxygen and sulfur

88refining processes 152–3rusting 109

saltsformation of 126ionic 59

separation of solutions 48sewage 57simple distillation 47smelting

of copper 110of iron 107

soaps 166sodium 101soil 55solar system 10solubility, solutions and solvents

45, 48, 59, 61–3stars 8–9steel manufacture 108sulfur 80–3, 88, 90

oxides of 84sulfuric acid 85–7

temperature, effect on reactionrates of 137–8

thorium series 188titration of acids 53–4transition metals 104–5

as catalysts 142

uranium series 186

water 56–9, 67, 87

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chemistry an illustrated guide to science

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