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I think I finally got it, after hearing 1000 times.

Long story short: in ground state and some similar,
electron's wavefunction is spherical, with a nucleus being at the center, which is exactly what can be considered a "collision".

The difference is that there're no such quantum numbers onboard both an electron and nucleus that would allow them to, say, annihilate, like in a case with positron.

Therefore, they're basically ignoring each other; except for EM interaction, of course.

And the shapes of orbitals? Well, they depend on just a kinetic energy of an electron.

..So, yeah :) question is, how incorrect is that.

Victor Novak
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2 Answers2

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There’s a lot of confusion here, so let me try to get to the heart of the matter the way I do with my general chemistry students. The key to seeing why electrons don’t cascade into the nucleus is not that they have to orbit in some particular shape, nor that they have to have any particular numbers describe the way they move. It is simply that the governing equation called the Heisenberg uncertainty principle requires that we cannot ever know the position and momentum of an electron simultaneously (or exactly at all). If the electron crashed into the nucleus, we would know that the electron has no momentum. This would violate the uncertainty principle. Thus, we are forced to make the rather bizarre proclamation that the electron is not a little ball, but actually is smeared out over a large amount of space all at the same time. The orbitals that chemists sometimes talk about electrons “occupying” might have accidentally confused you. The orbital is not a place the electron rattles around in; it is a description of what the electron is really like! And the shape of the electron orbitals certainly does not need to be spherical. For instance, consider a 2p orbital. So when we say the electron is in a 2p state, that means that the electron really is smeared out in a sort of weird dumbbell shape, and that it is likely to be on two opposite sides of the nucleus without ever actually being in between these locations! If this all seems weird, it is! Quantum mechanics is deeply weird and it will take a long time before you are comfortable and familiar with these ideas.

Matt Hanson
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If I understand correctly you are already happy with the idea that the electron is delocalised over the region around the nucleus, and that the uncertainty principle prevents it from shrinking down to a point. In that case your key question is related to your statement:

The difference is that there're no such quantum numbers onboard both an electron and nucleus that would allow them to, say, annihilate, like in a case with positron.

That is you are really asking why even though the electron overlaps with the proton it does not interact with the proton to form some new particle.

If this is the case then your statement is basically correct but with one exception - an electron can react with a proton to form a neutron. This reaction is energetically unfavourable so it does not happen in most atoms. However there are a few atoms where the conversion of the proton to a neutron increases the nuclear binding energy and this supplies enough energy for the reaction to happen. This process is called electron capture.

John Rennie
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