chemistry chapter 4

Chemistry ChapterChemistry Chapter 4 4

The Structure of The Structure of the Atoms the Atoms

Top Ten Top Ten

Table 3.1Table 3.1

Table Table 3.33.3

History of ChemistryHistory of Chemistry

• 400 B.C. Greeks proposed 4 elements– Earth– Fire– Water– Air

• Next 2000 years—alchemy• During this period discoveries were made

– Hg, S, Sb– prepared acids

Controversial Greek Controversial Greek ThinkingThinking!!

Democritus (460-370 B.C):-Matter is composed of “atomos” (now atoms)-Atoms were homogeneous & indivisible-Could not answer what holds atoms together

Aristotle (384 B.C.-322B.C.):-Matter was continuous and

indefinitely divisible (did not believe in atoms) -Matter made of earth, fire, air, & water-Idea was accepted for nearly 2000 years!

Indivisible or Divisible?Indivisible or Divisible?Democritis vs. AristotleDemocritis vs. Aristotle

Late 1700’sLate 1700’s

• Most chemists accepted element definition

• Understood elements combined to form compounds with various properties

• Disagreed whether compounds are always in the same ratio

What happened in 1790?What happened in 1790?

• Study of matter was revolutionized by new emphasis on Quantitative Analysis

• Aided by improved balances• Measurements were actually

ACCURATE!!!

Robert BoyleRobert Boyle

• Founder of Modern Chemistry (1627-1691)

• Took the “Al” out of Alchemy (although he started as one)

• First scientist to understand the importance of careful measurement

• Insisted science be based on experiments

• Famous for P=1/V

Antoine Lavoisier Antoine Lavoisier • Father of Modern

Chemistry (1743-1794)• Recognized and named

hydrogen and oxygen• Introduced the metric

system• Wrote first list of

elements and revised nomenclature

• Because of prominence in pre-revolutionary government, was beheaded at the height of the French revolution

John Dalton—Beginning of John Dalton—Beginning of Modern Atomic TheoryModern Atomic Theory

• Englishman from a Quaker family (1766-1844)

• Revolutionized chemistry by emphasizing that atoms can have weights and weights can be measured (quantitative)

• Opened a school at age 12

• Color blind/researched• Interested in botany• Theory not accepted

until 1905 Albert Einstein paper

Dalton’s Atomic Theory Dalton’s Atomic Theory (1808)(1808)

Atoms of a given element are identical in size, mass, and chemical properties.

Atoms of specific element are different from those of another element.

Different atoms combine in simple whole-number ratios to form compounds.

In chemical reactions, atoms are separated, combined, or rearranged

Matter is composed of extremely small particles called atoms

Atoms are indivisible and indestructible.

Dalton vs. Dalton vs. TodayTodayMatter is composed of extremely small particles called atoms.

True

Atoms are indivisible and indestructible.

Made up of smaller particles (protons, neutrons, & electrons)except in nuclear chemistry.

Atoms of a given elemet are identical in size, mass, and chemical properties.

Atoms of a given element have same p+ and e-, but may differ in # of neutrons

Atoms of a specific element are different from those of another element

True, how we identify them

Different atoms combine in simple whole-number ratios to form compounds

True, Law of Multiple Proportions

In chemical reactions, atoms are separated, combined, or rearranged

True

Law of Conservation of MassLaw of Conservation of Mass

Total mass of reactants =

Total mass of products

Antoine Lavoisier

Mass is neither created nor destroyed during chemical or physical reactions.

Law of Multiple ProportionsLaw of Multiple Proportions

• If two or more different compounds are composed of the same two elements, then the ratio is always small whole numbers. (CO, CO2)

What does this mean? (What does this mean? (Law of Law of Definite CompositionDefinite Composition))

• 50.0 g sample of pure H2O decomposed into its elements– would find 5.6 g H and 44.4 g oxygen – % mass would be:

mass H = 5.60 g x 100 = 11.2% Htotal mass 50.0 g

mass 0 = 44.4 g x 100 = 88.8% Ototal mass 50.0 g

Law of Definite (or Constant) Law of Definite (or Constant) CompositionComposition

• The fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound.

Figure 3.2:Figure 3.2: Representation of NO, NO Representation of NO, NO22, and , and NN22O.O.

What does an atom look like? (Sketch it on your paper!)

This is The Modern Atomic This is The Modern Atomic ModelModel

• Atom: The smallest particle of an element that retains the properties of the element

• Only seen by STM (Scanning Tunneling microscope)

Subatomic ParticlesSubatomic Particles

Particle Charge

Mass (amu) Location

Electron (e-)J.J.Thomson 1897Nobel Prize 1906Robert Milllikan (1910s)

-1 5.486x10-4

amu9.1 x 10-28 g1/1840 of H

Electron cloud

Proton (p+)Thomson/Goldstein-1907Rutherford 1920

+1 1.007 amu1.673 x 10-24 g

Nucleus

Neutron (no)Chadwick 1932Nobel Prize 1935

0 1.0091.675 x 10-24 g

Nucleus

Discovery of the ElectronDiscovery of the ElectronIn 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

Figure 3.7:Figure 3.7: Schematic of a cathode ray Schematic of a cathode ray tube.tube.

Some ModernSome ModernCCathode athode RRay ay TTubesubes

Mass of the ElectronMass of the Electron

1909 – Robert Millikan determines the mass of the electron.

The oil drop apparatus Mass of the

electron is 9.1 x 10-28 g

Conclusions from the Study Conclusions from the Study of the Electronof the Electron

Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.

Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons

Electrons have so little mass that atoms must contain other particles that account for most of the mass

Thomson’s Atomic Thomson’s Atomic ModelModel

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Based on the following facts: (1) atoms contain small, negatively charged particles called electrons and (2) the atoms of the element behave as if they have no charge at all

Ernest RutherfordErnest Rutherford

• 1871-1937• Learned physics in

JJ Thomson’s lab• Did much work

with alpha particles (+ charged part with mass)

• Most famous for his GOLD FOIL EXPERIMENT

Figure 3.5:Figure 3.5: Rutherford’s Rutherford’s experiment.experiment.

Try it Yourself!Try it Yourself!In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

The AnswersThe Answers

Target #1 Target #2

Figure 3.3:Figure 3.3: Plum Pudding model of an Plum Pudding model of an atom.atom.

Figure 3.6:Figure 3.6: Results of foil Results of foil experiment if experiment if Plum Pudding Plum Pudding

model had model had been correct.been correct.

Figure 3.6:Figure 3.6: Actual results. Actual results.

Rutherford’s FindingsRutherford’s Findings

The nucleus is small The nucleus is dense The nucleus is positively charged

Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected

“Like howitzer shells bouncing off of tissue paper!”

Conclusions:

Disbelievers….Disbelievers….• Albert Einstein when

to his grave not totally believing it

• According to classical physics, the electron would have collapsed into the nucleus

• 1910-1930 began the Quantum Physics Revolution (the physics of atomic and subatomic particles)

The Atomic The Atomic ScaleScale

Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud) Most of the volume of the atom is empty space

“q” is a particle called a “quark”

The Quark…The Quark…

Oops…wrong Quark!

About Quarks…About Quarks…Protons and neutrons are NOT fundamental particles.Protons are made of two “up” quarks and one “down” quark.Neutrons are made of one “up” quark and two “down” quarks.

Quarks are held togetherby “gluons”

Figure 3.9:Figure 3.9: A nuclear A nuclear

atom viewed atom viewed in cross in cross section.section.

Atomic NumberAtomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

Element # of protons Atomic # (Z)

Carbon 6 6

Phosphorus 15 15

Gold 79 79

IsotopeIsotopess

Elements occur in nature as mixtures of isotopes.Isotopes are atoms of the same element that differ in the number of neutrons

Figure 3.10:Figure 3.10: Two isotopes of Two isotopes of sodium.sodium.

Mass NumberMass NumberMass number is the number of protons and neutrons in the nucleus of an isotope.Mass # = p+ + n0

Nuclide p+ n0 e- Mass #

Oxygen - 10

- 33 42

- 31 15

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

Atomic Atomic MassesMasses

Isotope Symbol Composition of the nucleus

% in nature

Carbon-12

12C 6 protons6 neutrons

98.89%

Carbon-13


1.11%

Carbon-14


<0.01%

Atomic mass is the average of all the naturally isotopes of that element.Carbon = 12.011

Isotopes…Again Isotopes…Again (must be on the (must be on the test)test)

Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.Isotope Proto

nsElectron

sNeutron

sNucleus

Hydrogen–1

(protium)

1 1 0

Hydrogen-2

(deuterium)

1 1 1

Hydrogen-3

(tritium)

1 1 2

Chlorine Practice ProblemChlorine Practice Problem• Chlorine exists as 2 isotopes in

nature. Cl-35 (atomic mass 34.969 amu) has a 75.77% relative abundance. Cl-37 has an atomic mass 36.966 amu.

1. What is the % abundance of the Cl-37 isotope?


nature. Cl-35 (atomic mass 34.969 amu) has a 75.77% relative abundance. Cl-37 has an atomic mass 36.966 amu

Calculate the atomic mass of Chlorine.


nature. Cl-35 (atomic mass 34.969 amu) has a 75.77% relative abundance. Cl-37 has an atomic mass 36.966 amu.

How many times more massive is Cl-37 than Cl-35?

Atomic # and Atomic MassAtomic # and Atomic Mass

The Periodic LawThe Periodic Law

Chinese Periodic TableChinese Periodic Table

Triangular Periodic TableTriangular Periodic Table

““Mayan” Mayan” Periodic Periodic

TableTable

Stowe Periodic TableStowe Periodic Table

A Spiral Periodic TableA Spiral Periodic Table

• First International Congress of Chemists– 60 to 70 of 113 elements had been

discovered– Italian chemist Cannizzaro presented

method for measurement of atomic mass that all could agree on.

The Year 1860….The Year 1860….

John Newlands (1837-1898)

• English chemist that in 1864 proposed an organizational scheme for the elements

• Noticed properties repeated periodically every 8 elements

• Called “Law of Octaves”– Did not work for all elements– Criticized analogy for being “non-

scientific”

– Writing a book about the same time.

– Wanted to include new information of atomic masses

– Wanted to find an arrangement for all of the information on the 60-70 elements

– Lothar Meyer (German chemist) did the same but Mendeelev published first

Dimitri MendeleevDimitri Mendeleev

Modern Russian TableModern Russian Table

– Properties of the elements recur in regular cycles (periodically) when the elements are arranged in order of increasing atomic mass.

Law of Mendeleev:Law of Mendeleev:

Missing?Missing?

14Si

28.09

??

50Sn

118.71

Named missing element “Ekasilicon”

From base word “eka” meanging next in order

““Ekasilicon”Ekasilicon”

Predicted Properties

Observed Properties

Atomic Mass 72 amu

Density 5.5 g/cm3

Melting Point 825° C



Observed Properties

Atomic Mass 72 amu 72.61 amu

Density 5.5 g/cm3 5.32 g/cm3

Melting Point 825° C 938° C



Observed Properties

Oxide Formula XO2 GeO2

Chloride Formula

XCl4 GeCl4

Mendeleev’s Periodic TableMendeleev’s Periodic Table

Dmitri Mendeleev

Henry Moseley (1887-1915)

• After more elements were discovered, order of atomic mass wasn’t working

• 1913: Discovered atoms have unique number or protons in nucleus and rearranged table in order of atomic number

• Periodic Law: The statement that there is a periodic repetition of chemical and physical properties of elements when they are arranged by increasing atomic number.

The Periodic TableThe Periodic Table

Period

Group or family

PeriodGroup or Family

Figure 3.12:Figure 3.12: Elements Elements classified classified

as metals and nonmetals.as metals and nonmetals.

Properties of MetalsProperties of Metals Metals have luster (shiny) when smooth and clean

Metals are solid @ room T

Metals are good conductors of heat and electricity

Metals are malleable

Metals are ductile

Metals have high tensile strength

Located left of stairstep

Figure 3.17:Figure 3.17: Spherical atoms packed closely Spherical atoms packed closely together.together.

• Mostly brittle solids• Properties between metal and non-

metal (semi-conductors)• Found in nature only as compounds• Once obtained as free metals, are

stable in the presence of air

Metalloids:Metalloids:

PropertiesProperties of Nonmetalsof Nonmetals

Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle and dull looking if solid Many nonmetals are gases at room T

Examples of NonmetalsExamples of Nonmetals

Sulfur, S, was once known as “brimstone”

Microspheres of phosphorus, P, a reactive nonmetal

Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure

Figure 3.14:Figure 3.14: Nitrogen gas contains N Nitrogen gas contains N22 molecules.molecules.

Figure 3.13:Figure 3.13: A collection of argon A collection of argon atoms.atoms.

Figure 3.14:Figure 3.14: Oxygen gas contains O Oxygen gas contains O22 molecules.molecules.

Table 3.5Table 3.5

Valence e-

• The e- in an element’s outermost orbital; they determine the chemical properties of the element.

• Group 1: 1 valence e-








Figure 3.19:Figure 3.19: The ions formed by selected The ions formed by selected members of groups 1, 2, 3, 6, and 7.members of groups 1, 2, 3, 6, and 7.

Atomic Radius

• Metal: one half the distance between two adjacent atoms in a crystal

• Non-metal: half the idstance between nuclei of identical atoms that are chemically bonded together.

• Trends:• Atomic radii generally decreases left to

right across a period (more e-, same E level)

• Atomic radii generally increases down a group (added e- and added E level)

Ionic Radius

• Ion: An atom or a group of atoms that has a charge (due to loss or gain of e-)

– Cations (+ charged ions)•Radii become smaller due to loss of e-

and decreased repulsion/often lose E level

– Anions (- charged ions)•Radii become larger due to increase in

# of e- and repulsion among them (w/o change in proton #)

Table of Ion SizesTable of Ion Sizes

Octet Rule

• Atoms tend to gain, lose, or share e- in order to acquire a full set of 8 valence e-.

Electronegativity

• The relative ability of an element’s atoms to attract e- in a chemical bond.

• Defined in Paulings units– F: most electronegative element– Fr: least electronegative element– Noble Gases: none

Trends• E.N. increases across a period• E.N. decreases down a group

Ionization E

• The E required to remove an e- from a gasseous atom

• The lower the I.E, the more easily an atom given away its e-.

• Trends– I.E. increases from left to right– I.E. decreases from top to bottom

Figure 3.11:Figure 3.11: The periodic table The periodic table

Figure 3.20:Figure 3.20: Pure water does not conduct a Pure water does not conduct a current.current.

Figure 3.20:Figure 3.20: Water containing Water containing dissolved salt dissolved salt

conducts a current.conducts a current.

Radioactivity

• Radioactivity: a process in which some substance spontaneously emit radiation

• Radiation: The rays and particles emitted by the radioactive materials.

• Nuclear Reaction: A change in an atom’s nucleus.

• Radioactive Decay: emitted radiation in a spontaneous process

• Major Breakthrough: 1890’s.• Only happens in radioactive atoms with

unstable nuclei

Types of Radiation

• Alpha Radiation– Made up of alpha particles– Deflected toward a negatively charged

plate• Beta Radiation

– Made up of beta particles– Deflected toward a positively charged plate

• Gamma Radiation– High E radiation that has no charge and

mass– Not deflected by electronic or magnetic

fields

AllotropesAllotropes

• Different forms of a given element• Different properties b/c different

arrangement of atoms• EX: diamond, graphite,

Buckminsterfullerene (All Carbon!) • Look in your book—p. 70

Periodic Table with Group NamesPeriodic Table with Group Names

chemistry chapter 4

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