Chapter 7

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Chapter 7
Atomic Structure
Dr. S. M. Condren
ELECTROMAGNETIC RADIATION
Dr. S. M. Condren
Electromagnetic Spectrum
Dr. S. M. Condren
Electromagnetic Radiation
Electromagnetic wave
• A wave of energy having a frequency
within the electromagnetic spectrum and
propagated as a periodic disturbance of
the electromagnetic field when an electric
charge oscillates or accelerates.
Dr. S. M. Condren
Electromagnetic Radiation
Electromagnetic wave
• wavelength
• frequency
• amplitude
Dr. S. M. Condren
Electromagnetic Radiation
Figure 7.1
Dr. S. M. Condren
Wave motion: wave length and nodes
Dr. S. M. Condren
Wave Nature of the Electron
Dr. S. M. Condren
Electromagnetic Radiation
• Waves have a frequency
• Use the Greek letter “nu”,
units are “cycles per sec”
, for frequency, and
l
• Use the Greek letter “lambda”, , for
wavelength, and units are “meters”
• All radiation:
l• = c
• c = velocity of light = 3.00 x 108 m/sec
• Long wavelength --> small frequency
• Short wavelength --> high frequency
Dr. S. M. Condren
Electromagnetic Radiation
Long wavelength --> small frequency
Short wavelength --> high frequency
increasing
frequency
increasing
wavelength
Dr. S. M. Condren
Fireworks
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Flame Tests
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The Electric Pickle
• Excited atoms can emit light.
• Here the solution in a pickle is
excited electrically. The Na+ ions
in the pickle juice give off light
characteristic of that element.
Dr. S. M. Condren
Line Emission Spectrum
Dr. S. M. Condren
Electromagnetic Radiation
Example: Calculate the frequency, , of
red light that has a wavelength, l, of
700. nm.
 = (1/700. nm)(109nm/1m)(3.00x108m/sec)
= 4.29x1014 s-1
= 4.29x1014 cycles/s
= 4.29x1014 hertz
Dr. S. M. Condren
Electromagnetic Radiation
Short wavelength -->
high frequency
high energy
Long wavelength -->
small frequency
low energy
Dr. S. M. Condren
Black Body Radiation
http://www.cbu.edu/~mcondren/C11599/BBvis.mov
Dr. S. M. Condren
Photoelectric Effect
Experiment demonstrates the particle nature of light.
Dr. S. M. Condren
Energy of Radiation
Energy of 1.00 mol of photons of red light.
E = h•
= (6.63 x 10-34 J•s)(4.29 x 1014 s-1)
= 2.85 x 10-19 J per photon
E per mol =
(2.85 x 10-19 J/ph)(6.02 x 1023 ph/mol)
= 171.6 kJ/mol
This is in the range of energies that can break
bonds.
Dr. S. M. Condren
Spectra
Line Spectrum
• A spectrum produced by a luminous gas or
vapor and appearing as distinct lines
characteristic of the various elements
constituting the gas.
Emission Spectrum
• The spectrum of bright lines, bands, or
continuous radiation characteristic of and
determined by a specific emitting substance
subjected to a specific kind of excitation.
Absorption Spectrum
• Wavelengths of light that are removed from
transmitted light.
Dr. S. M. Condren
Atomic Line Emission Spectra
and Niels Bohr
Bohr’s greatest contribution
to science was in building
a simple model of the
atom. It was based on an
understanding of the
Niels Bohr
(1885-1962)
SHARP LINE
EMISSION SPECTRA
of excited atoms.
Dr. S. M. Condren
Atomic Spectra and Bohr
Bohr said classical view is wrong.
e- can only exist in certain discrete
orbits — called stationary states.
e- is restricted to QUANTIZED energy
states.
Energy of state = - C/n2
where n = quantum no. = 1, 2, 3, 4, ....
Dr. S. M. Condren
Bohr Atom
Dr. S. M. Condren
Energy States
Ground State
• The state of least possible energy in a
physical system, as of elementary
particles. Also called ground level.
Excited States
• Being at an energy level higher than the
ground state.
Dr. S. M. Condren
Energy Adsorption/Emission
Active Figure 7.11
Dr. S. M. Condren
Atomic
Spectra and
Bohr
∆E = -(3/4)C
C has been found from experiment (and is now
called R, the Rydberg constant)
R (= C) = 1312 kJ/mol or 3.29 x 1015 cycles/sec
so, E of emitted light
= (3/4)R = 2.47 x 1015 sec-1
and l = c/ = 121.6 nm
This is exactly in agreement with experiment!
Dr. S. M. Condren
Line Emission Spectra
of Excited Atoms
High E
Short l
High 
Low E
Long l
Low 
Visible lines in H atom spectrum are
called the BALMER series.
Dr. S. M. Condren
Origin of Line Spectra
Paschen series
Balmer series
Active Figure 7.12
Dr. S. M. Condren
Atomic Line Spectra
and Niels Bohr
Niels Bohr
(1885-1962)
Bohr’s theory was a great
accomplishment.
Rec’d Nobel Prize, 1922
Problems with theory —
• theory only successful for H.
• introduced quantum idea
artificially.
• So, we go on to QUANTUM or
WAVE MECHANICS
Dr. S. M. Condren
Quantum or Wave Mechanics
Schrodinger applied idea of ebehaving as a wave to the problem
of electrons in atoms.
He developed the WAVE
EQUATION
Solution gives set of math
expressions called WAVE
E. Schrodinger
FUNCTIONS, 
1887-1961
Each describes an allowed energy
state of an eQuantization introduced naturally.
Dr. S. M. Condren
WAVE FUNCTIONS, 
• is a function of distance and two
angles.
• Each  corresponds to an
ORBITAL — the region of space
within which an electron is found.
•  does NOT describe the exact
location of the electron.
• 2 is proportional to the probability
of finding an e- at a given point.
Dr. S. M. Condren
Uncertainty Principle
W. Heisenberg
1901-1976
•Problem of defining nature
of electrons solved by W.
Heisenberg.
•Cannot simultaneously
define the position and
momentum (=m*v) of an
electron.
•We define e- energy
exactly but accept limitation
that we do not know exact
position.
Dr. S. M. Condren
Types of Orbitals
s orbital
p orbital
Dr. S. M. Condren
d orbital
Orbitals
• No more than 2 e- assigned to an orbital
• Orbitals grouped in s, p, d (and f) subshells
s orbitals
also
p orbitals
d orbitals
f orbitals
Dr. S. M. Condren
s orbitals
p orbitals
d orbitals
f orbitals
p orbitals
d orbitals
f orbitals
1
3
5
7
2
6
10
14
s orbitals
No.
orbs.
No. e-
Dr. S. M. Condren
QUANTUM NUMBERS
The shape, size, and energy of each orbital is
a function of 3 quantum numbers:
n (principal) =>
l (angular) =>
ml (magnetic) =>
shell
subshell
designates an orbital
within a subshell
s (spin) => designates the direction of spin
Dr. S. M. Condren
QUANTUM NUMBERS
Symbol
ValuesDescription
n (principal)
1, 2, 3, ..
l (angular)
ml (magnetic)
s (spin)
Orbital size and energy
where E = -R(1/n2)
0, 1, 2, .. n-1 Orbital shape or type
(subshell)
-l..0..+l
Orbital orientation
# of orbitals in
subshell = 2 l + 1
-1/2 or +1/2 Direction of spin of electron
Dr. S. M. Condren
Types of
Atomic
Orbitals
Dr. S. M. Condren
Atomic Orbitals
• Types of orbitals found in the known
elements: s, p, d, and f
• schools play defensive football
• Packer version: secondary pass defense
fails
Dr. S. M. Condren
S Orbitals
1s
2s
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3s
p Orbitals
The three p orbitals lie 90o apart
in space
Dr. S. M. Condren
2px Orbital
3px Orbital
Dr. S. M. Condren
d Orbitals
3dxy Orbital
3dxz Orbital
3dx2- y2 Orbital
Dr. S. M. Condren
3dyz Orbital
3dz2 Orbital
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