An electron is bound to the nucleus by the electromagnetic force, but is not a round ball, but a wave distribution of probabilities.
I don't know if it's the actual case, but I've been thinking of all "particles" like "waves" in a pool. Small disturbances in the fields (e.g. electromagnetic), like jumping in a pool. The electron IS the disturbance, because to us that is what we can measure (and we can only measure one place at a time). So the electron doesn't rotate around the nucleus - instead its a wave in the same area where the nucleus is. The electron's "probability wave" disturbs the space around the nucleus - including inside it, and 1000 miles away from it. It's just has way more disturbance in certain places - AKA "the shell" its in. Just like any wave, it "fades" with distance but who's to say where the wave ends.
In fact, that wave isn't exactly the same for every electron. Each "shell" is waving at a different amplitude (is amplitude the right analogy?) - and you can only have so many "waves" add up in a shell simply because there's no more room because of the length of each wave (like a spiral-o-graph). You can only put another wave in the gaps of the previous wave (if you did put two in the same place, it would double and be part of the next shell, right?). And when an electron's amplitude changes, e.g. is lowered, the total energy can't be destroyed, so the difference is emitted as another wave of the difference - that wave is a photon. And the same applies when a photon is added to that wave. Like rowing in the water - the exiting wave and the rowed wave is added together. I think of Photons are partial Electrons. They are like the "wake" of an electrons wave change.