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27.7 Wave-particle Duality

Experiments show light has wave properties or particle properties.

Diffraction Interference Photoelectric effect Compton scattering

Einstein → Eparticle = hfwave

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27.8 Wave Nature of Matter

Do particles have wave properties?

De Broglie wavelength of a particle

Not noticed for macroscopic objects but important for microscopic objects

Diffraction of electrons from a crystal Shown for other subatomic particles as well

phλ

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X-ray diffraction 1912 Electron diffraction 1927

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27.10 Early Models of the Atom Plum-pudding model and Rutherford’s

experiment

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27.10 Early Models of the Atom 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

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)

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

2

i2f n

1n1R

λ1

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27.12 The Bohr Model 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.... 3, 2, 1, n 2πnhmvrn

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27.12 The Bohr Model

m)(0.529x10nr -102n

2n neV 13.6E

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27.13 The de Broglie Hypothesis