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Chapter 12:
Quantum
Mechanics and
Atomic Theory
o
Electromagnetic
Radiation
o
Quantum Theory
o
Particle in a Box
o
The Hydrogen Atom
o
Quantum Numbers
o
Orbitals
o
Many Electron Atoms
o
Periodic Trends
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Big Idea:
The structure of atoms
must be explained
using quantum
mechanics, a theory in
which the properties of
particles and waves
merge together.
Chapter 12: Quantum Mechanics and Atomic Theory
Electromagnetic Radiation
Electromagnetic Radiation:
Consists of oscillating
(timevarying)electric and magnetic fields that
travel through space at
2.998 × 10
8
?
?
(c = speed
of light) or just over 660 million mph.
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Note: All forms of radiation transfer energy from one region of space into another.
Examples of Electromagnetic Radiation:
•
Visible light
•
Radio Waves
•
XRays
Chapter 12: Quantum Mechanics and Atomic Theory
Electromagnetic Radiation
Wavelength
(λ):
Is the
peaktopeak distance.
Amplitude:
Determines
brightness of the
radiation.
Frequency
(ν): The
number of cycles per
second (
1 𝐻? = 1
1
?
).
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Note: Changing the wavelength changes the
region of the spectrum (i.e. xray to visible).
Chapter 12: Quantum Mechanics and Atomic Theory
Electromagnetic Radiation
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Chapter 12: Quantum Mechanics and Atomic Theory
Quantum Theory
If white light is passed
through a prism, a
continuous spectrum
of light is found.
However, when the
light emitted by
excited hydrogen
atoms is passed
through a prism the
radiation is found to
consist of a number
of components or
spectra lines.
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Chapter 12: Quantum Mechanics and Atomic Theory
Quantum Theory
Black Body:
An object that absorbs and emits all
frequencies of radiation without favor.
Heated Black Bodies
𝑻𝝀
?𝒂𝒙
= ?. ????
𝑰
???
= ?. ?? × ??
−?
𝑾
?
?
?
?
𝑻
?
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Note:
λ
max
is the most prevalent wavelength not the longest wavelength.
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Chapter 12: Quantum Mechanics and Atomic Theory
Quantum Theory
Theory
Scientists used classical physics arguments to
derive an expression for the energy density
(Rayleigh Jens Law).
????𝑔? ????𝑖?? ∝
𝑇
?
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The Problem With Explaining Black Body Radiation
Using Classical Mechanics
Classical mechanics put
no limits on minimum
wavelength therefore at
very small
?
,
?
would be a
huge value even for low temperatures.
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Chapter 12: Quantum Mechanics and Atomic Theory
Quantum Theory
Max Plank:
Proposed that the exchange
of energy between matter and radiation
occurs in quanta, or packets of energy.
His central idea was that a charged
particle oscillating at a frequency
?
, can
exchange energy with its surroundings by
generating or absorbing electromagnetic
radiation only in discrete packets of
energy.
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Quanta:
Packet of energy (implies minimum
energy that can be emitted).
Charged particles oscillating at a frequency,
?
,
can only exchange energy with their
surroundings in discrete packets of energy.
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 Winter '08
 Watts
 Atom

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