[chris_l]

So shouldn't the electron density be a sphere? It has this strange ring around outside...

[colanderman]

The 2D projection of a spherical shell isn't a uniform disc – it does indeed look more or less like a ring. (Consider the rough analogy of a swinging pendulum – it spends most of its time near the edges of its swing.)

[Thrymr]

An orbital is not a spherical shell.

Edit: These are probably higher energy states. e.g., the 6s orbital: http://en.wikipedia.org/wiki/File:HydrogenOrbitalsN6L0M0.png

edit 2: Previous comment was still not correct. More plots of electron density for different energy states: http://cronodon.com/Atomic/AtomTech4.html

[JoeAltmaier]

Hydrogen electrons 'orbit' in shells, not a uniform sphere