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Chapter 3

Atoms and Moles

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Atomic Models

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3.1 Matter Made of Atoms

Atomic Theory

Mikhail Lomonosov (1711-1795)and Antoine Lavosier (1743-1794): developed law ofconservation of mass

states that mass of reactants

equals mass of products

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Law of Conservation of Mass

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Law of Conservation of Mass

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Atomic Theory

Joseph Proust (1754-1826):proposed law of definiteproportions

states that two samples of agiven compound are made of

the same elements in exactlythe same proportions by mass

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Atomic Theory

Claude-Louise Berthollet (1748-1822): proposed law ofmultiple proportions

states that when twoelements combine to form two

or more compounds, the massof one element that combineswith a mass of the other is in

the ratio of small whole #s

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Daltons Atomic Theory

John Dalton (1766-1844):developed a new atomic theory

1. all matter is made of atoms,which cannot be subdivided,created, or destroyed

2. atoms of a given elementare identical in their chemicaland physical properties

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3. atoms of different elementsdiffer in their physical andchemical properties

4. atoms of different elementscombine in simple, whole-

number ratios to formcompounds

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5. in chemical reactions,atoms are combined,separated, or rearranged butnot created, destroyed, orchanged

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Further Progress

Jons Berzelius (1779-1848)

studied proportions in which

elements combine with oneanother (over 2000)

experimental underpinning

of Daltons theorymade table of atomic weights

named halogens

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Further Progress

Jons Berzelius (1779-1848)

invented alphabetical

nomenclature of elementscoined terms organicchemistry, catalysis, and

protein

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Further Progress

valency and bonding describedin 1850s

Stanislao Cannizzaro(remember?): distinctionbetween atoms and molecules

periodic table developed in1860s

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3.2 Structure of Atoms

Subatomic Particles

Heinrich Geissler (1814-1879):invented the vacuum tube (late1850s)

vacuum tube: hollow, glasstube in which the air has been

removed; electrodes at eitherend

produces a glow when current

flows between electrodes

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Subatomic Particles

Eugen Goldstein (1850-1930)

named glowing rays cathode

rays (1876)showed that they weredeflected by magnetic fields;

could cast shadowsdiscovered rays coming fromanode; called them canal

rays (1886)

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Subatomic Particles

William Crookes (1832-1919)

showed that cathode rays

were made of particles, notlight (1879)

convincing to the British, but

not mainlanders

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Subatomic Particles

J. J. Thomson (1856-1940):showed that rays were slowerthan light (1894)

Jean Perrin (1870-1942):showed that metal plates hit by

rays became negatively charged(1895)

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Three Random Walks

f

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Subatomic Particles

J. J. Thomson (again)

measured mass/charge; found

that particles were small orcharge was large (1897)

measured electric charge

itself; found electrons to be1/2000 mass of a H atom(1899)

new atomic model

fl f h d

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Deflections of Cathode Rays

h i d l

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Thomsons Atomic Model

3 2 S f A

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Subatomic Particles

Ernest Rutherford (1871-1937)

discovered and radiation

(1890s)discovered radiation (1900)

discovered that particles are

a He nucleus (1908)

R di ti

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, , Radiation

R di ti I

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Radiation Image

3 2 St t f At

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Subatomic Particles

Ernest Rutherford (1871-1937)

gold foil experiment (1909)

particles fired at gold foil

most went through, somedeflected

conclusion: most of themass and charge of anatom is in the nucleus;electrons in cloud

G ld

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Gold

G ld F il E i t

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Gold Foil Experiment

E t ti R lit

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Expectations versus Reality

E l ti

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Explanation

E l ti

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Explanation

R th f d P

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Rutherfords Paper

3 2 St ct e of Atoms

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Subatomic Particles

Francis Aston (1877-1945):showed that atoms come indifferent varieties (differentweights) (1912)

called isotopes: atoms with

the same number of protonsbut different numbers ofneutrons

E.R. discovered proton (1918)

Evidence for Isotopes

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Evidence for Isotopes

3 2 Structure of Atoms

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Subatomic Particles

James Chadwick (1891-1974):discovered the neutron (sort of)(1932)

3 3 Electron Configuration

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3.3 Electron Configuration

Electrons and Light

Light as a moving wave

c= f

c speed of light = 3 x 108

m/s

wavelength (m)

distance between peak ortroughs of a wave

f frequency (1/s 1 hertz) # of waves er second

Waves

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Waves

Light Waves

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Light Waves

Light

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Light


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Electrons and Light

Albert Einstein (1879-1955)

atoms emit or absorb EMradiation in discrete(quantized) units (1905)

light has properties of waves

and particles (1905)


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Electrons and Light

Niels Bohr (1885-1962)

worked with Rutherford

new atomic model: electronsorbit nucleus at particularenergy levels (1912)

electrons dont give off energy(no spiraling allowed)

Why dont electrons go

strai ht to the nucleus???


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Electrons and Light

Bohrs model

electron in state of lowestpossible energy is in groundstate

if electron gains energy, it

moves to an excited state(!)if electron falls back to groundstate, it releases energy as

light

Excited State

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Excited State

Absorbance and Emission

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Quantization

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Quantization


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Electrons and Light

Bohrs model, continued

Bohr predicted thewavelengths of light forhydrogenhe was right!

all light wavelengths together

are called line-emissionspectrum

each element has its own

Hydrogen Emission

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Hydrogen Emission

H Absorbance and Emission

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H Absorbance and Emission


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Electrons and Light

Louis de Broglie (1892-1987)

particles can be described aswaves (1925)

therefore, electrons can onlyhave certain frequencies

(energy levels) and cant falltoward nucleus

quantum atomic model


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Quantum numbers

n principal (main energylevels)

l angular momentum (shapeor type of sublevel)

l= 0 sorbital

l= 1 porbitall= 2 dorbital

l= 3 forbital

Principal Quantum Number

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Principal Quantum Number

Energy Level Transitions

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Energy Level Transitions


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Quantum numbers

ml magnetic (subset oflquantum number)

ms spin (orientation of

magnetic field) +1/2 or -1/2

Quantum Numbers

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Quantum Numbers

Orbital Shapes

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Orbital Shapes


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Electron Configurations

Pauli exclusion principle:each orbital can hold no morethan two electrons

no two electrons can have thesame four quantum numbers

Aufbau principle: electrons fillorbitals that have the lowestenergy first

1s

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Overlapping Orbital Energies


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Electron Configurations

Hunds rule: orbitals of thesame nand lnumber areoccupied by one electron before

pairing occurs

Hunds Rule

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Hund s Rule

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