| MadSci Network: Physics |
It's important to distinguish the "old quantum theory" -- including the Bohr Model that you seem to be referring to at first -- from a more modern interpretation (using the Schrodinger equation, from which you get 1s orbitals, etc.)
The whole-wave-multiple-per-orbit idea pre-dated the Schrodinger equation, and you are correct: those orbits should never intersect the nucleus. But solving the Schrodinger equation yields a spherically-symmetric solution that is actually peaked at the nucleus! (This is the so-called 1s orbital, or electron "cloud".) So you're right that these two pictures are quite different; the latter one is generally accepted, and the former one has been mostly discarded except as a bridging concept between classical and quantum physics.
That said, there are a few connections that I can note between these two different pictures. Even for the Schrodinger equation solution that corresponds to the 1s orbital/cloud, there is still a "wave" of sorts, because there is an oscillation in time that is normally not mentioned (because it doesn't have any observable consequences; it is just an overall phase). The frequency of this oscillation matches the frequency of the electron wave in the Bohr model. Also, the radius of the n=1 orbital in the Bohr model (known as the Bohr radius) happens to be the most likely measurement of the distance between the electron and the proton in a Hydrogen atom.
Finally, for your last question, those solutions only represent 1 electron, not 2. As soon as you have 2 electrons (say, in the Helium atom), the Schrodinger equation becomes impossible to solve exactly, because of the interactions between the two electrons.
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