I don't know a whole lot about quantum mechanics so this is more of a common sense answer. In the first energy there is one orbital. Since there aren't any others electrons can be in a wide range of places. However, when you go to the second evergy level, there are 4 orbitals. They repulse each other. That is why their shapes get narrower. Also, since they a repulsed by electrons in other energy levels, they will be farther and farther from the nucleus.
This is only a model though, to help us visualize. Like Nick said, we need to stop thinking about atoms as definite shapes.
(though I personally don't like the quantum mechanical model and think that something better is bound to come along)
|