Rutherford, explain!
Accelerating charges ought to loose energy in the form of γ rays.
What, then, makes the atom stable?
Rutherford, explain!
Even if the atom did loose energy, it should have been continuous...
... which it wasn't.
We need a better theory.
Bohr's Postulates
 Electrons in atoms orbit the nucleus in circular orbits.
 There exists discrete stationary orbits in which the electrons orbit stably without radiating.
 It turns out that the angular momentum of these orbits are multiples of ħ
 When electrons jump from orbit to orbit, they emit/lose energy according to Plank radiation.
Radius

Equating Centrapetal Force and Electric Force,

From Bohr's second postulate,

Therefore,

And we have the radius,
Velocity
Plugging in the radius gives the velocity,
Energy

Kinetic Energy:

Potential Energy:

Total Energy:
Matter Waves
 Matter does behave like a wave, in some sense.
 deBroglie hypothesised that the associated wavelength of a particle is given by λ = h/p
Matter Waves
Seen carefully enough, electrons produce diffraction patterns.
deBroglie's Justification
 Bohr's orbitals are stationary states where the wave function does not evolve.
 Consider an electron wavicle of n wavelengths wrapped around a Bohr orbit.
Not the end...
 Still too many spectral lines
 What if there is more than one electron?
 Too classical: Newtonian mechanics is hardly a good way to describe phenomenon at the quantum level.
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