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Chapter 12 Quantum Mechanics and Atomic Theory
12.1 Electromagnetic Radiation
A.
Electromagnetic Radiation:
radiant energy that exhibits wavelike behavior and
travels through space at the speed of light in a vacuum. Has electric and magnetic
fields that simultaneously oscillate in planes mutually perpendicular to each other
and to the direction of propagation through space.
B. Waves are characterized by wavelength, frequency, and speed.
Wavelength:
the
distance between two consecutive peals or troughs in a wave. Frequency: the
number of waves (cycles) per second that pass a given point in space. Short
wavelength radiation must have a high frequency. (Waves with the shortest
wavelength have the highest frequency and waves with the longest wavelength
have the lowest frequency.) There is an inverse relationship between wavelength
and frequency. (
c
= νλ) Where c is the speed of light (constant 2.99792458 X10
8
),
v is the frequency in cycles per second, and λ is the wavelength in meters. (Hertz,
Hz, is cycles per second.)
12.2 The Nature of Matter
A.
Blackbody radiation: radiation that originates from the thermal energy of the body
only. Ultraviolet catastrophe: predicts a radiation profile that has no maximum and goes
to infinite intensity at very short wavelengths.
B.
Planck’s constant: 6.626 X10
34
J s. The change in energy for a system ∆
E
can be
represented by the equation ∆
E
=
nhv
, where
n
is and integer,
h
is Plank’s constant, and
v
is the frequency of the electromagnetic radiation absorbed or emitted.
C.
Energy is quantized and can only be transferred in discrete units of size
hv
. Each
of these small “packets” of energy is called a quantum. A system can transfer energy only
in whole quanta. Thus energy seems to have particulate properties.
D.
Photon: a quantum of electromagnetic radiation. The energy of a photon is
calculated by: E
photon
=
hv
=
hc
/λ, where
h
is Planck’s constant,
v
is the frequency of the
radiation and λ is the wavelength of the radiation.
E.
Photoelectric effect: the phenomenon in which electrons are emitted from the
suface of a metal when light strikes it. The following observations characterize the
photoelectric effect.
1.
Studies in which the frequency of the light is carried show that no
electrons are emitted by a given metal below a specific threshold
frequency
v
o
.
2.
For light with frequency lower than the threshold frequency, no
electrons are emitted regardless of the intensity of the light.
3.
For light with frequency greater than the threshold frequency, the
number of electrons emitted increases with the intensity of the light.
4.
For light with frequency greater than the threshold frequency, the
kinetic energy of the emitted electrons increases linearly with the
frequency of the light.
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View Full DocumentThese observations can be explained by assuming that electromagnetic radiation
in quantized (consists of photons), and that the threshold frequency represents the
minimum energy required to remove the electron from the metal’s surface.
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 Fall '07
 Fakhreddine/Lyon
 Chemistry, Atom

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