[andrewas]

Willow has it right. It does get even more complex in a couple years though.

Each electron shell consists of electron orbitals, each electron orbital contains up to two electrons. 1 "p" type, 3 "d" types and 5 "f" types if memory serves. Which is probably dosent, and theres one after "f" which totaly escapes me. The designation isnt important anyway, the principle is.

Now, you know that shells have different energy levels, right?

Well, the orbitals within those shells also have slightly varying energy levels, and in the higher shells p type orbitals have less energy than the f types from the previous level. Since its, strictly speaking, orbitals and not shells that fill up in order of energy level, the "p" type in shell "M" fills up before the "f" types in shell "N"

Now are you glad that you dont have to study the theory behind all this for another couple years? Anyway, I usualy find it easier to remember stuff like this by learning the reason why, so maybe some of this will be useful.