Structure and Isotopes

Helium has two non-radioactive isotopes, Helium-3 and Helium-4.  These isotopes occur naturally.  There are three naturally occurring radioactive isotopes, but these have no commercial use.

Helium has never been known to form compounds with any other element and no compound has ever been manufactured.    

Helium's electronic configuration is 1s².  It has two electrons in its valence shell but is inert.               

Helium is stable and because of the fact that it is inert it has been named one of the noble gases.

http://www.chemicalelements.com/elements/he.html

This is an image of how helium is structured.  The "P" stands for the number of protons. and the "N" stands for the number of neutrons.