cavity

Yep, is it that obvious. You, my friend, hit the nail directly on the head. Like maybe a sort of a two-in-one donkeypunch kind of nail, head, whatever!!! Ahh!

I am a nerd:

1s2
2s2 2p6
3s2 3p6
4s2 3d10 4p6
5s2 4d10 5p5

or [Kr] 5s2 4d10 5p5 for short. count it up, it's all there.

that diagram isn't the structure though. it's just a schematic representation of the electronic configuration, i.e. what I wrote. you should check out the quantum mechanical atomic structure. it's really big and highly polarisable.