Forgive me if the answer to this is obvious. I have no formal physics training, and I remember that when I asked my physics teacher this, she just frowned and said "Good question."
An electron is negatively charged. A proton is positively charged. Based on basic principles, it seems like it would be logical for the electron cloud of an atom to "collapse" into the nucleus and become a part of it (especially since the electrons are so much lower mass). Why doesn't this happen? How do electrons maintain separation from the protons in the nucleus, when the opposite chargers ought to draw them together?
I considered that perhaps the charge in the electron was too minuscule in comparison to the proton (like having a negatively charged magnet on Saturn while all of Earth was positively charged; obviously the magnet wouldn't just be drawn to the Earth because the forces weren't strong enough to act over that distance). But if that was or is the case, I would expect some other chemical behaviors to not exist. For example, the whole phenomenon of water being a "dipole". If the charge of the electron is too weak to interact with the proton, how could the oxygen in water more strongly attract them than hydrogen? I get that the oxygen has more protons, and thus more positive charge in the nucleus, but that still would seem to support that the oxygen atom's own electrons should be attracted to it...
Can anyone explain the phenomena occurring here or simply point out the flaw in my thinking?