Chapter 7
Atomic Structure
and Periodicity
Section 7.1
Electromagnetic Radiation
 Much of our understanding of the structure of the
atom comes from observations of how matter
interacts with light.
 These studies began the field of quantum
mechanics and helped develop our current model
of the atom.
Section 7.1
Electromagnetic Radiation
 Electromagnetic radiation is the emission and transmission
of energy in the form of electromagnetic waves.
 Maxwell (1873) proposed that visible light consists of
electromagnetic waves.
 Light, one type of electromagnetic radiation, is one of the
ways that energy travels through space.
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Section 7.1
Electromagnetic Radiation
For All electromagnetic
radiation:
c = ln
λ = Wavelength (lambda)
distance between identical points on successive waves.(m)
ν = Frequency (nu)
number of waves (cycles) per sec in s -1 or hertz (Hz)
c = velocity or speed of light in a vacuum
a constant: 2.998×108 m/s
 Wavelength and frequency are inversely related
4
Section 7.1
Electromagnetic Radiation
long λ = low ν = low energy
short λ = high ν = high energy
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Section 7.1
Electromagnetic Radiation
The Electromagnetic Spectrum
   Increasing Wavelength   
   Increasing Frequency   
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6
Section 7.1
Electromagnetic Radiation
Example: Photosynthesis uses light with a frequency of
4.54 x 1014 s-1. To what wavelength, in nm, does this
correspond?
c = ln
λ =
c
ν
=
2.998 x 108 m/s
4.54 x 1014m
= 6.60 x 10-7 m
λ = 6.60 x 10-7 m
x
1 x 109nm = 660. nm
1m
“Heated Solids Problem”
Solved by Planck in 1900
When solids are heated, they emit electromagnetic radiation
over a wide range of wavelengths.
Radiant energy emitted by an object at a certain temperature
depends on its wavelength.
Energy (light) is emitted or absorbed in discrete units (quantum).
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Section 7.2
The Nature of Matter
The energy, E, of electromagnetic radiation is directly
proportional to the frequency (ν) of the radiation.
Ephoton = hν
E = Energy, in Joules (kg·m2/s2)
h = Planck’s constant = 6.626 × 10-34 J·s
ν = Frequency (s-1 or Hertz, hz)
 Planck’s constant, h, is the quantity of energy that can
be absorbed or emitted.
 Energy is not continuous, it is quantized, meaning it can
be gained or lost only in integer multiples of hν.
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9
Section 7.2
The Nature of Matter
 Einstein proved that light has a
wave and particle nature. He
proposed that electromagnetic
radiation is quantized. E
(energy) has mass (only in the
relativistic sense).
 Electromagnetic energy can be
viewed as a stream of particles.
The energy of each photon can
be given by: E = mc2
Section 7.2
The Nature of Matter
 The smallest unit of electromagnetic
radiation that can be emitted is essentially a
small “packet” of energy called a ‘quantum’
or ‘photon’.
 Combining these two formulas:
c = ln
We get:
Ephoton = hν
Ephoton = hc
λ
Section 7.2
The Nature of Matter
Example: The laser in an audio compact disc player uses light
with a wavelength of 7.80 x 102 nm.
A) Calculate the frequency of the radiation.
λ = 7.80 x 102 nm x
ν= c =
λ
1m
1 x 109nm
2.998 x 108 m/s
7.80 x 10-7m
= 3.84 x 1014 s-1
= 7.80 x 10-7m
Section 7.2
The Nature of Matter
Example: The laser in an audio compact disc player uses light
with a wavelength of 7.80 x 102 nm.
B) What is the energy of this radiation per photon?
E =
hc =
λ
(6.626 x 10-34Js)(2.998 x 108 m/s)
7.80 x 10-7m
= 2.55 x 10-19 J
Section 7.2
The Nature of Matter
 Einstein arrived at this conclusion through his analysis of
the photoelectric effect.
 In the photoelectric effect, incident light ejects electrons
from the material.
 This requires the photon to have sufficient energy to eject
the electron.
Section 7.2
The Nature of Matter
 Photoelectron spectroscopy
determines the energy needed to
eject electrons from the material and
provides a method to determine the
structure of an atom.
 The intensity of the photoelectron is a
measure of the number of electrons
in that energy level
KE = hn - W
where W is the work function and
depends how strongly electrons
are held in the metal
hn
KE e-
Section 7.2
The Nature of Matter
The Photoelectric effect
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16
Section 7.2
The Nature of Matter
Wavelength can be related to mass:
 Combine these two equations: E = mc2
E = hc
λ
 Gives m = h
λc
 However, for a particle not moving at the speed of light,
c, but rather at some velocity, v, de Broglie’s equation is:
m= h
λv
or
λ = h
mv
Section 7.2
The Nature of Matter
Dual nature of light:
 Electromagnetic radiation exhibits both particle and
wave properties.
 Light travels through space as a wave, and transmits
energy as a particle.
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18
Section 7.2
The Nature of Matter
Example: What is the wavelength, in nm, of an electron
(mass = 9.11 x 10-31 kg) traveling at 5.31 x 106 m/s?
λ = h
mv
=
6.626 x 10-34 Js
(9.11 x 10 -31 kg)( 5.31 x 106 m/s)
λ = h
mv
=
6.626 x 10-34 (kg m2/s2) s
(9.11 x 10-31 kg)( 5.31 x 106 m/s)
λ = 1.37 x 10-10 m
= 1.37 x 10-1 nm
Section 7.2
The Nature of Matter
 The End!
Section 7.2
The Nature of Matter
Section 7.2
The Nature of Matter
 Quantum Mechanics: Fabric of the Cosmos –
Documentary
 http://www.youtube.com/watch?v=qYil-x1wAtE
 https://www.youtube.com/watch?v=sYRX9O3abM&feature=youtube_gdata_player
 introduction to quantum physics
 http://www.youtube.com/watch?v=L0UAO7UZkc
g