chapter two: atoms, molecules, and ions. copyright © houghton mifflin company. all rights reserved....

Chapter Two:

ATOMS, MOLECULES, AND IONS

Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 2

Early History of Chemistry

• Greeks were the first to attempt to explain why chemical changes occur.

• Alchemy dominated for 2000 years:– Several elements discovered– Mineral acids prepared

• Robert Boyle was the first “chemist”:– Performed quantitative experiments

2.1


Three Important Laws

• Law of conservation of mass (Lavoisier):– Mass is neither created nor destroyed

• Law of definite proportion (Proust):– A given compound always contains exactly the

same proportion of elements by mass

2.2


Three Important Laws (continued)

• Law of multiple proportions (Dalton):– When two elements form a series of

compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers

– http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/003_MULTIPLEPROP.MOV

2.2

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Dalton’s Atomic Theory (1808)

• Each element is made up of tiny particles called atoms.

2.3


Dalton’s Atomic Theory (continued)

• The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.

2.3



• Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms.

2.3



• Chemical reactions involve reorganization of the atoms—changes in the way they are bound together.

• The atoms themselves are not changed in a chemical reaction.

2.3


Concept Check

Which of the following statements regarding Dalton’s atomic theory are still believed to be true?

I. Elements are made of tiny particles called atoms.

II. All atoms of a given element are identical.

III. A given compound always has the same relative

numbers and types of atoms.

IV. Atoms are indestructible.


Early Experiments to Characterize the Atom

• J. J. Thomson (1898-1903):– Postulated the existence of electrons using

cathode-ray tubes– Determined the charge-to-mass ratio of an

electron– The atom must also contain positive particles

that balance exactly the negative charge carried by the electrons

2.4

Figure 2.8 Deflection of Cathode Rays by an Applied Electric Field

Figure 2.9 The Plum Pudding Model of the Atom



• Robert Millikan (1909):– Performed experiments involving charged oil

drops– Determined the magnitude of the electron

charge– Calculated the mass of the electron

2.4

Figure 2.10 A Schematic Representation of the Apparatus Millikan Used to Determine

the Charge on the Electron

Milikan’s Experiment

• http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/004_MILLIKANOIL.MOV

• Perform Millilkan’s Experiment yourself– http://webphysics.davidson.edu/applets/pqp_pr

eview/contents/pqp_errata/cd_errata_fixes/section4_5.html


http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/004_MILLIKANOIL.MOV



http://webphysics.davidson.edu/applets/pqp_preview/contents/pqp_errata/cd_errata_fixes/section4_5.html





• Ernest Rutherford (1911):– Explained the nuclear atom– Atom has a dense center of positive charge

called the nucleus– Electrons travel around the nucleus at a

relatively large distance

2.4

Figure 2.12 Rutherford's Experiment On a-Particle Bombardment of Metal Foil

Rutherford’s experiment

• http://micro.magnet.fsu.edu/electromag/java/rutherford/

• Animation with narration– http://cwx.prenhall.com/petrucci/medialib/medi

a_portfolio/text_images/006_RUTHERFORD.MOV


http://micro.magnet.fsu.edu/electromag/java/rutherford/

http://micro.magnet.fsu.edu/electromag/java/rutherford/

http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/006_RUTHERFORD.MOV



Rutherford’s Observations

• Most α particles passed straight through the foil

• Some α particles were deflected to the side

• A few α particles were bounced backward


Figure 2.13 a & b (a) Expected Results of the Metal Foil Experiment

if Thomson's Model Were Correct (b) Actual Results

Rutherford’s Conclusions

• Atoms are mostly empty space

• Atoms contain positively charged particles

• Atoms contain a dense nucleus



The Modern View of Atomic Structure-Nuclear Model

• The atom contains: Electrons Protons – found in the nucleus; positive charge

equal in magnitude to the electron’s negative charge

Neutrons – found in the nucleus; no charge; virtually same mass as a proton

2.5


The Modern View of Atomic Structure

• The nucleus is:– Small compared with the overall size of the

atom– Extremely dense; accounts for almost all of the

atom’s mass

2.5


Nuclear Atom Viewed in Cross Section


The Modern View of Atomic Structure

• Isotopes:– Atoms with the same number of protons but

different numbers of neutrons– Show almost identical chemical properties;

chemistry of atom is due to its electrons– In nature most elements contain mixtures of

isotopes

2.5


Two Isotopes of Sodium

2.5

Isotope Symbols

XAZ

• X = Element symbol

• Z = Atomic Number = number of protons

• A = Mass Number = protons + neutrons



Exercise

A certain isotope X contains 54 electrons and 78 neutrons.

What is the mass number of this isotope?

What is the symbol of this isotope?

2.5/2.6

Ions

• Atoms that have gained or lost electrons

• Gained electrons– Negative charge– Anion

• Lost electrons– Positive charge– Cation


• Cations

• Mg2+

– Lost 2 electrons

• K+ – Lost 1 electron

• Anions

• F-

– Gained 1 electron

• S2-

– Gained 2 electrons



Chemical Bonds

• Covalent Bonds: – Bonds form between atoms by sharing

electrons– Resulting collection of atoms is called a

molecule

2.6


Covalent Bonding

2.6


Chemical Bonds

• Ionic Bonds: Bonds form due to force of attraction between

oppositely charged ions Ion – atom or group of atoms that has a net

positive or negative charge Cation – positive ion; lost electron(s) Anion – negative ion; gained electron(s)

2.6


Molecular vs. Ionic Compounds

2.6


The Periodic Table

• Metals vs. Nonmetals

• Groups or Families – elements in the same vertical columns– Alkali metals, alkaline earth metals, halogens,

and noble gases

• Periods – horizontal rows of elements

2.7


The Periodic Table

2.7


Naming Compounds

• Binary Compounds:– Composed of two elements

• Binary Ionic Compounds:– Metal-nonmetal

• Binary Covalent Compounds:– Nonmetal to nonmetal

2.8


Binary Ionic Compounds (Type I)

• Cation is always named first and the anion second.

• Monatomic cation has the same name as its parent element.

• Monatomic anion is named by taking the root of the element name and adding –ide.

2.8


Binary Ionic Compounds (Type I)

• Examples:

KCl Potassium chloride

MgBr2 Magnesium bromide

CaO Calcium oxide

2.8

Chemical Formulas

• Identify the elements present– Element symbols

• Identify the number of each atom– Subscripts

• Aluminum sulfide Al2S3

– 2 Al atoms for every 3 S atoms

Writing the Formulas from the Names

–Determine the ions present

–Determine the charges on the cation and anion

–Balance the charges to get the subscripts

Writing the Formulas from the Names (cont.)

• Magnesium chloride– Mg2+ Cl-

– Total positive charge must equal total negative charge

– 1 Mg2+ will balance 2Cl-

– MgCl2


Polyatomic Ions

• Ions consisting of two or more covalently bonded atoms

• Examples of compounds containing polyatomic ions:

NaOH Sodium hydroxide

Mg(NO3)2 Magnesium nitrate

(NH4)2SO4 Ammonium sulfate

2.8

Compounds Containing Polyatomic Ions

• Polyatomic ions are charged entities that contain more than one atom

• Polyatomic compounds contain one or more polyatomic ions

• Name polyatomic compounds by naming cation and anion

• Al(C2H3O2)3 = aluminum acetate


Binary Ionic Compounds (Type II)

• Metals in these compounds form more than one type of positive charge.

• Charge on the metal ion must be specified.

• Roman numeral indicates the charge of the metal cation.

• Transition metal cations usually require a Roman numeral.

2.8

Determining the Charge on a Cation – Au2S3

• Determine the charge on the anion– Sulfide = -2

• Determine the total negative charge– (-2) x 3 = -6

• Total positive charge = total negative charge

• Divide total positive charge by the number of cations– +6/2 = +3


Binary Ionic Compounds (Type II)

• Examples:

CuBr Copper(I) bromide

FeS Iron(II) sulfide

PbO2 Lead(IV) oxide

2.8

Type IIBinary Ionic Compounds (cont.)

¶Old naming system

¶Uses root name or latin name for metal

¶Uses suffixes instead of roman numerals


¶Suffixes

¶_____ic for higher charge

¶_____ous for lower charge


¶Examples

¶Iron (III) chloride = ferric chloride

¶Iron (II) chloride = ferrous chloride


¶Common latin names

¶Cu – cupric, cuprous

¶Pb – plumbic, plumbous

¶Sn – stannic, stannous

¶Fe – ferric, ferrous


• For Type II

Determine the charges on the cation and anion

• Charge on cation = roman numeral

–Balance the charges to get the subscripts


• Copper (I) oxide– Cu+1 O-2

– 2 Cu+1 will balance 1 O-2

– Cu2O


Formation of Ionic Compounds

2.8


Binary Covalent Compounds (Type III)

• Formed between two nonmetals.• First element is named first, using the full

element name.• Second element is named as if it were an

anion.• Prefixes are used to denote the numbers of

atoms present.• Prefix mono- is never used for naming the

first element.2.8

Table 2.6 Prefixes Used to Indicate Number in Chemical Names


Binary Covalent Compounds (Type III)

• Examples:

CO2 Carbon dioxide

SF6 Sulfur hexafluoride

N2O4 Dinitrogen tetroxide

2.8

Writing the Formulas from the Names

• For Type III compounds, use the prefixes to determine the subscripts

• Carbon tetrachloride = CCl4


Overall Strategy for Naming Chemical Compounds


Flowchart for Naming Binary Compounds


Acids

• Acids can be recognized by the hydrogen that appears first in the formula—HCl.

• Molecule with one or more H+ ions attached to an anion.

2.8


Acids

• If the anion does not contain oxygen, the acid is named with the prefix hydro- and the suffix -ic.

• Examples:

HCl Hydrochloric acid

HCN Hydrocyanic acid

H2S Hydrosulfuric acid

2.8


Acids

• If the anion does contain oxygen:– The suffix -ic is added to the root name if the

anion name ends in -ate.

• Examples:

HNO3Nitric acid

H2SO4 Sulfuric acid

HC2H3O2 Acetic acid

2.8


Acids

• If the anion does contain oxygen:– The suffix -ous is added to the root name if the

anion name ends in -ite.

• Examples:

HNO2Nitrous acid

H2SO3 Sulfurous acid

HClO2 Chlorous acid

2.8


Flowchart for Naming Acids


Exercise

Which of the following compounds is named incorrectly?

a) KNO3 potassium nitrate

b) TiO2 titanium(II) oxide

c) Sn(OH)4 tin(IV) hydroxide

d) PBr5 phosphorus pentabromide

e) CaCrO4 calcium chromate

2.8

chapter two: atoms, molecules, and ions. copyright © houghton mifflin company. all rights reserved....

Documents

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applied electric field

atoms of different elements

types of atoms

daltons atomic theory

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given element