Was the first model to explain the Balmer series, notably linking atomic spectra to the Planck constant and therefore to other initial quantum mechanical observations.
This was one of the first major models that just said:
I give up, I can't tie this to classical physics in any way, let's just roll with it, OK?
It still treats electrons as little points spinning around the nucleus, but it makes the non-classical postulate that only certain angular momentums (and therefore energies) are allowed.
Bagic jump between orbitals in the Bohr model. Analogous to the later wave function collapse in the Schrödinger equation.
Refinement of the Bohr model that starts to take quantum angular momentum into account in order to explain missing lines that would have been othrwise observed TODO specific example of such line.
They are not observe because they would violate the conservation of angular momentum.
TODO confirm year and paper, Wikipedia points to: zenodo.org/record/1424309#.yotqe3xmjhe