Why doesnt an electron get pulled in toward the nucleus?

Well, in terms of classical physics, an electron orbits the nucleus due to the electrical force. But the theory of electromagnetism tells us that accelerating charged particles lose energy, and anything which is orbiting something is accelerating. So, put these two facts together and the electron should lose energy and spiral into the nucleus. This obviously doesn't happen (if it did, there would be no atoms...), so this was a serious problem for physics in the first decade or so of the 20th century. The semi-classical explanation, created by a physicist named Bohr to solve the problems with the classical explanation, proposed that electrons could only be in orbits where the quantity called angular momentum (which is numerically the momentum of a particle times the radius of its orbit, or formulaicly pr=mvr=m(r^2)w where w is the angular velocity [think of it as the frequency of the orbit]) was some integer number times a constant (called h-bar). This theory prevented the electron from falling into the nucleus of an atom, and it explained the Hydrogen atom perfectly. But it didn't work for any other kind of atom. Finally, there's the quantum explanation, which emerged about ten/fifteen years or so after Bohr did his work. In quantum theory particles are represented by probability distributions called wavefunctions (which is, depending on how you approach it, either a result of or the reason for Heisenburg's Uncertainty Principle; also, I'm playing a bit fast and loose with my terminology: a wavefunction isn't a probability distribution, but if you basically square the wavefunction, that's the probability distribution). Now, if you work out the wavefunction of an electron around a nucleus, it turns out to be constant in time, which means that it doesn't fall into the nucleus (or fly off into space or whatever else; it stays around the nucleus as desribed by the wavefunction). Of course, one thing which is interesting to note is that in many situations (incluing the simplest) the signle point (though not the radius) where the probability of finding the electron is the highest is actually in the nucleus. :) But if you found the electron there at one moment the next moment you could easily find it outside the nucleus. It's random (as far as we know).