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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,
follow Hunds rule.
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
Periodic Properties: Atomic Radii
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Chapter 3/53
Electron Configurations and
Periodic Properties: Atomic Radii
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 3/54
Electron Configurations and
Periodic Properties: Atomic Radii
radiusrow
radiuscolumn
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Chapter 3/55