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Chapter 29
Atoms and
Molecules
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PowerPoint® Lectures for
College Physics: A Strategic Approach, Second Edition
29 Atoms and Molecules
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Slide 29-2
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Spectroscopy
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Continuous Spectra and Blackbody Radiation
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Discrete Spectra of the Elements
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The Hydrogen Spectrum
Wavelengths of
visible lines in the
hydrogen spectrum
Balmer’s formula
91.1 nm
λ
 1 1
 2 2
m n 
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Rutherford’s Experiment
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Using the Nuclear Model
Ionization
The nucleus
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Isotopes
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Bohr’s Model of Atomic Quantization
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Bohr’s Model of Atomic Quantization (cont’d)
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Frequencies of Photons Emitted in Electron
Transitions
Eatom
fphoton 
h
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Representing Atomic States
Energy-level diagram
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The Bohr Hydrogen Atom
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Energy-Level Diagram of the Hydrogen Atom
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The Quantum-Mechanical Hydrogen Atom
1. Schrödinger found that the energy of the hydrogen atom is
given by the same expression found by Bohr, or
En  
13.60 eV
n2
n  1, 2,3,...
The integer n is called the principal quantum number.
2. The angular momentum L of the electron’s orbit must be one of
the values
L  l (l  1) U
l  0,1, 2,3,..., n  1
The integer l is called the orbital quantum number.
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The Quantum-Mechanical Hydrogen Atom (cont’d)
3. The plane of the electron’s orbit can be tilted, but only at
certain discrete angles. Each allowed angle is characterized
by a quantum number m, which must be one of the values
m  l , l  1,...,0,..., l  1, l
The integer m is called the magnetic quantum number
because it becomes important when the atom is placed in a
magnetic field.
4. The electron’s spin can point only up or down. These two
orientations are described by the spin quantum number ms,
which must be one of the values
1
1
ms   or 
2
2
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Energy and Angular Momentum of the Hydrogen
Atom
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Energy Levels in Multielectron Atoms
Hydrogen atom
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Multielectron atom
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Excited States and the Pauli Exclusion Principle
Helium atom
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Lithium atom
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The Periodic Table
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Building Up the Periodic Table
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Excitation by Absorption and Collision
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Emission Spectra
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Checking Understanding
Suppose that an atomic excited state decays to the ground state
by emission of two photons, with energies E1 and E2. Is it possible
for that excited state to decay to the ground state by emission of
a single photon with energy E1 + E2?
A. It is always possible, for every atom.
B. It is never possible, for any atom.
C. It is always possible for hydrogen atoms, but is
unlikely for other atoms.
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Answer
Suppose that an atomic excited state decays to the ground state
by emission of two photons, with energies E1 and E2. Is it possible
for that excited state to decay to the ground state by emission of
a single photon with energy E1 + E2?
A. It is always possible, for every atom.
B. It is never possible, for any atom.
C. It is always possible for hydrogen atoms, but is
unlikely for other atoms.
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Molecules
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Fluorescence
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Checking Understanding
Which of the following is not a possible fluorescence process?
A.
B.
Absorption of red light and emission of green light
Absorption of ultraviolet light and emission of infrared
light
C. Absorption of ultraviolet light and emission of green light
D. Absorption of blue light and emission of red light
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Answer
Which of the following is not a possible fluorescence process?
A. Absorption of red light and emission of green light
B. Absorption of ultraviolet light and emission of infrared
light
C. Absorption of ultraviolet light and emission of green light
D. Absorption of blue light and emission of red light
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Stimulated Emission and Lasers
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Photon Amplification
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A Helium-Neon Laser
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