27.7 Wave-particle Duality

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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

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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 Rutherfords experiment

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• 27.10 Early Models of the Atom
• Rutherfords 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

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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 Bohrs 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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• 27.12 The Bohr Model

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• 27.13 The de Broglie Hypothesis