Noble gases possess eight valence electrons, except for helium, which has only two valence electrons. Valence electrons are the electrons in the outermost energy level (also known as the valence shell) of an atom. The noble gases belong to Group 18 (VIII A) of the periodic table, also known as the noble gas group or the helium group. Their electron configurations are very stable, as they have completely filled valence shells. This stability is the reason why noble gases are generally unreactive and rarely form chemical bonds with other elements.