How do I make this object orbit around the center without making it turn
Try this:


  
  Parent the atom to the ring or a null in the center
  Rotate the ring/null which will rotate the electron around the middle
  Apply an expression to the rotation property of the electron layer
  


Rotation Expression:

parent.transform.rotation * -1


This simple expression will rotate the electron in the opposite direction from its parent (ring/null) layer, which keeps the minus from rotating.

Hope this helps!