Bonding

We've been discussing bonding in class, specifically ionic bonding.  You'll notice that I've added a few websites that may interest you, one of which should be a big help in understanding the balancing act required when making ionic bonds.  For your visual pleasure, here's a picture illustrating the changes in atomic radius the sodium and chlorine atoms undergo upon ionization.

My challenge to you, for five bonus points:  Describe why the atomic radius of sodium shrinks when it loses an electron, while that of chlorine gets larger when it gains an electron.