1. The end of classical physics: photons, electrons, atoms
Last time:
Discovery of the electron: Charge quantization
photo-electric effect: light behaves as a particle
Discovery of the nucleus: Rutherford scattering experiment
Today:
Atomic spectra: emission and absorption. Evidence for atomic energy levels
Bohr’s model of the hydrogen atom
Continuous emission: black-body radiation

2. Phhoto-electric effect:
The energy transfer is all or nothing process in contrast to the classical theory of continuous transfer of energy
eV0 = Kmax = hf –E0

3. Rutherford’s model Continuous spectrum
Then the electron FALLS into the nucleus: catastrophe !
But this doesn’t happen => the catastrophe is in classical physics !

4. Atomic spectra: emission and absorption
Spectra are discrete
Different atoms have different lines
Absorption and emission spectra are NOT the same

5. Hydrogen atom: Bohr’s model
Stable orbits, with distinct quantum numbers n= 1,2,3…
Angular momentum is quantized :

6. Emission and absorption
Balmer found ( by trial and error) :