Transcript Slide 1

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27.7 Wave-particle Duality
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Experiments show light has wave properties or
particle properties.
Diffraction
 Interference
 Photoelectric effect
 Compton scattering
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Einstein → Eparticle = hfwave
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27.8 Wave Nature of Matter
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Do particles have wave properties?
De Broglie wavelength of a particle
λ 
h
p
Not noticed for macroscopic objects but important
for microscopic objects
Diffraction of electrons from a crystal
 Shown for other subatomic particles as well
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X-ray diffraction 1912
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Electron diffraction 1927
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27.10 Early Models of the Atom
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Plum-pudding model and Rutherford’s experiment
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27.10 Early Models of the Atom
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Rutherford’s “planetary model” - the atom is mostly
empty space with a small positive nucleus.
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27.11 Atomic Spectra
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27.11 Atomic Spectra
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Each element has its own distinct set of spectral
“lines” – like human fingerprints or UPC labels
Helium was discovered in the Sun (1868) before on
the Earth (1882)
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The solar spectrum has lines that were not known on the
Earth at that time
Applications: astronomy, chemistry, forensics, …
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27.11 Atomic Spectra
 1
1 
 R  2  2 
λ
ni 
 nf
1
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27.12 The Bohr Model
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Why do atoms only emit and absorb at certain
wavelengths? Why are atoms stable?
Assumptions of Bohr’s theory
1. The e- moves in circular orbits around the nucleus
 2. Only certain orbits are stable
 3. Radiation is emitted when the e- “jumps” from a higher
energy state to a lower one.
 4. The size of the orbits is determined by the e- orbital
angular momentum.
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mvr
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n

nh
2π
n  1, 2, 3, ...
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27.12 The Bohr Model
rn  n (0.529x10
2
En 
-10
m)
 13.6 eV
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n
2
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27.13 The de Broglie Hypothesis
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