Chem4Kids.com: Atoms: Orbitals

The “K” shell is the one closest to the nucleus, and “Q” is the farthest away. For simple atoms, those “n” values usually match the row number on the periodic table and are also known as energy levels. The second description looks at how electrons act inside of the shells. There are certain patterns of movement.

http://www.chem4kids.com/files/atom_orbital.html