Customizable Atom: Choose the number of electrons and it generates you an atom represented in the Bohr model.

This is just a simple model of an atom: It just fills the rings with electrons (this is not correct for every element!)
For a more Customizable atom with full control over every ring, please visit:
http://www.thingiverse.com/thing:113015

Thank you Damrin for pointing it out, that my "simple" atom was not correct for every element!

Edit: There is a remix of this Thin with pre-configured Atoms and Text!
http://www.thingiverse.com/thing:114247