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John E. McMurry Robert C. Fay

Lecture NotesAlan D. EarhartSoutheast Community College Lincoln, NE

General Chemistry: Atoms First

Chapter 3Periodicity and the Electronic Structure ofAtoms

Copyright 2010 Pearson Prentice Hall, Inc.

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Chapter 3/2

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/3

Light and the Electromagnetic

SpectrumElectromagnetic energy (light) is characterized by

wavelength, frequency, and amplitude.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/6

Light and the Electromagnetic

Spectrum

Wavelength x Frequency = Speed

=

m

s

m

s1

cx

cis defined to be the rate of travel of all

electromagnetic energy in a vacuum

and is a constant valuespeed of light.

c= 3.00 x 108

sm

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/7

Light and the Electromagnetic

Spectrum

The light blue glow given off by mercury streetlamps

has a wavelength of 436 nm. What is the frequency in

hertz?

436 nm

3.00 x 108 sm

1 x 109 nm

1 m

c=

=

= 6.88 x 1014 s-1 = 6.88 x 1014 Hz

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/8

Electromagnetic Energy and

Atomic Line Spectra

Line Spectrum: A series of discrete lines on an

otherwise dark background as a result of light emitted

by an excited atom.

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Chapter 3/9

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Chapter 3/10

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/11

1= R

n2

1

m2

1-

Electromagnetic Energy and

Atomic Line Spectra

Johannes Rydberg later modified the equation to fit

every line in the entire spectrum of hydrogen.

Johann Balmer in 1885 discovered a mathematical

relationship for the four visible lines in the atomic line

spectra for hydrogen.

R (Rydberg Constant) = 1.097 x 10-2 nm-1

1

= R n21

22

1-

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/12

Particlelike Properties of

Electromagnetic Energy

Photoelectric Effect: Irradiation of clean metal

surface with light causes electrons to be ejected from

the metal. Furthermore, the frequency of the light used

for the irradiation must be above some threshold

value, which is different for every metal.

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Chapter 3/13

Particlelike Properties of

Electromagnetic Energy

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/14

Particlelike Properties of

Electromagnetic Energy

Einstein explained the effect by assuming that a beam

of light behaves as if it were a stream of particlescalledphotons.

Photoelectric Effect: Irradiation of clean metal

surface with light causes electrons to be ejected from

the metal. Furthermore, the frequency of the light used

for the irradiation must be above some threshold

value, which is different for every metal.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/15

Particlelike Properties of

Electromagnetic Energy

E

Quantum: The amount of energy corresponding

to one photon of light.

h (Plancks constant) = 6.626 x 10-34 J s

Electromagnetic energy (light) is quantized.

E= h

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/16

Particlelike Properties of

Electromagnetic Energy

Niels Bohr proposed in 1914 a model of the hydrogen

atom as a nucleus with an electron circling around it.

In this model, the energy levels of the orbits are

quantized so that only certain specific orbitscorresponding to certain specific energies for the

electron are available.

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Chapter 3/17

Particlelike Properties of

Electromagnetic Energy

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/18

Wavelike Properties of Matter

The de Broglie equation allows the calculation of a

wavelength of an electron or of any particle or object

of mass m and velocity v.

mv

h=

Louis de Broglie in 1924 suggested that, iflightcan

behave in some respects like matter, then perhaps

mattercan behave in some respects like light.

In other words, perhaps matter is wavelike as well asparticlelike.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/19

Quantum Mechanics and the

Heisenberg Uncertainty Principle

In 1926 Erwin Schrdinger proposed the quantum

mechanical model of the atom which focuses on the

wavelike properties of the electron.

In 1927 Werner Heisenberg stated that it is impossibleto know precisely where an electron is and what path

it followsa statement called the Heisenberg

uncertainty principle.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/20

Wave Functions and Quantum

NumbersProbability of finding

electron in a region

of space ( 2)

Wave

equation

Wave function

or orbital ( )

solve

A wave function is characterized by three parameterscalled quantum numbers, n, l, ml.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/21

Principal Quantum Number (n)

Describes the size and energy level of the orbital

Commonly called shell

Positive integer (n = 1, 2, 3, 4, )

As the value ofn increases: The energy of the electron increases

The average distance of the electron from the

nucleus increases

Wave Functions and Quantum

Numbers

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/22

Wave Functions and Quantum

NumbersAngular-Momentum Quantum Number (l)

Defines the three-dimensional shape of the orbital

Commonly called subshell

There are n different shapes for orbitals

Ifn = 1 then l= 0 Ifn = 2 then l= 0 or 1

Ifn = 3 then l= 0, 1, or2

etc.

Commonly referred to by letter (subshell notation)

l= 0 s (sharp) l= 1 p (principal)

l= 2 d(diffuse)

l= 3 f(fundamental)

etc.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/23

Wave Functions and Quantum

NumbersMagnetic Quantum Number (ml )

Defines the spatial orientation of the orbital

There are 2l+ 1 values ofmland they can have

any integral value from -lto +l

Ifl= 0 then ml= 0 Ifl= 1 then ml= -1, 0, or 1

Ifl= 2 then ml= -2, -1, 0, 1, or2

etc.

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Wave Functions and Quantum

Numbers

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Chapter 3/25

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Chapter 3/26

The Shapes of Orbitals

Node: A surface of zero

probability for finding

the electron.

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Chapter 3/27

The Shapes of Orbitals

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The Shapes of Orbitals

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/31

Quantum Mechanics and

Atomic Line Spectra

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Electron Spin and the Pauli

Exclusion PrincipleElectrons have spin which gives rise to a tiny

magnetic field and to a spin quantum number (ms).

Pauli Exclusion Principle: No two electrons in an

atom can have the same four quantum numbers.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/34

Electron Configurations of

Multielectron AtomsElectron Configuration: A description of which

orbitals are occupied by electrons.

Degenerate Orbitals: Orbitals that have the same

energy level. For example, the threep orbitals in agiven subshell.

Ground-State Electron Configuration: The lowest-

energy configuration.

Aufbau Principle (building up): A guide for

determining the filling order of orbitals.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/35

Electron Configurations of

Multielectron AtomsRules of the aufbau principle:

1. Lower-energy orbitals fill before higher-energy

orbitals.

2. An orbital can only hold two electrons, which musthave opposite spins (Pauli exclusion principle).

3. If two or more degenerate orbitals are available,

Hunds Rule: If two or more orbitals with the same

energy are available, one electron goes into each until

all are half-full. The electrons in the half-filled orbitals

all have the same value of their spin quantum number.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/36

Electron Configurations of

Multielectron Atoms

n = 1s orbital (l= 0)

1 electronH: 1s1

Electron

Configuration

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/37

1s2

n = 1

s orbital (l= 0)

2 electrons

Electron Configurations of

Multielectron Atoms

H:

He:

Electron

Configuration

1s1

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/38

n = 2

s orbital (l= 0)

1 electrons1s2 2s1

Electron Configurations of

Multielectron Atoms

H:

Li:

Lowest energy to highest energy

He:

Electron

Configuration

1s2

1s1

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/39

Electron Configurations of

Multielectron Atoms

N:

n = 2

p orbital (l= 1)

3 electrons

H:

1s2 2s2 2p3

Li:

He:

Electron

Configuration

1s2 2s1

1s2

1s1

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/40

Electron Configurations of

Multielectron Atoms

N:

H:

Li:

1s

He:

Electron

Configuration

Orbital-Filling

Diagram

1s2 2s2 2p3

1s2 2s1

1s2

1s1

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/41

Electron Configurations of

Multielectron Atoms

N:

H:

Li:

1s

1sHe:

Electron

Configuration

Orbital-Filling

Diagram

1s2 2s2 2p3

1s2 2s1

1s2

1s1

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/42

Electron Configurations of

Multielectron Atoms

N:

H:

Li:

1s

1s

2s1s

He:

Electron

Configuration

Orbital-Filling

Diagram

1s2 2s2 2p3

1s2 2s1

1s2

1s1

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/43

Electron Configurations of

Multielectron Atoms

N:

H:

He:

Li:

Orbital-Filling

Diagram

1s

1s

2s1s

1s 2p2s

Electron

Configuration

1s2 2s2 2p3

1s2 2s1

1s2

1s1

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/44

Electron Configurations of

Multielectron Atoms

Na: [Ne] 3s11s2 2s2 2p6 3s1

Ne configuration

Electron

Configuration

Shorthand

Configuration

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/45

Electron Configurations of

Multielectron Atoms

Na:

P:

[Ne] 3s11s2 2s2 2p6 3s1

1s2 2s2 2p6 3s2 3p3 [Ne] 3s2 3p3

Electron

Configuration

Shorthand

Configuration

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/46

Electron Configurations of

Multielectron Atoms

Na:

P:

K:

[Ne] 3s11s2 2s2 2p6 3s1

1s2 2s2 2p6 3s2 3p3

1s2 2s2 2p6 3s2 3p6 4s1

[Ne] 3s2 3p3

[Ar] 4s1

Ar configuration

Electron

Configuration

Shorthand

Configuration

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/47

Electron Configurations of

Multielectron Atoms

Sc:

Na:

P:

1s2 2s2 2p6 3s2 3p6 4s2 3d1

K:

Shorthand

Configuration

Electron

Configuration

[Ar] 4s1 3d1

[Ne] 3s11s2 2s2 2p6 3s1

1s2 2s2 2p6 3s2 3p3

1s2 2s2 2p6 3s2 3p6 4s1

[Ne] 3s2 3p3

[Ar] 4s1

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Chapter 3/48

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/49

Some Anomalous Electron

Configurations

[Ar] 4s1 3d5Cr:

Cu: [Ar] 4s1 3d10

Actual

Configuration

Expected

Configuration

[Ar] 4s2 3d4

[Ar] 4s2 3d9

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/50

Electron Configurations and

the Periodic TableValence Shell: Outermost shell.

Br: 4s2 4p5Cl: 3s

2

3p5

Na: 3s1Li:

2s

1

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Chapter 3/52

Electron Configurations and

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Chapter 3/53

Electron Configurations and

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/54

Electron Configurations and

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Chapter 3/55

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