If you knew the number of valence electrons in a nonmetal atom, how would you determine the valence of the element?

Basically, nitrogen has 5 valence electrons and it needs 3 more valence electrons to be able to obtain a complete octet. Thus, after the bond, N2 contains 8 valence electrons.
N2 is a chemical formula of Nitrogen gas. Nitrogen is called N2 and not N because it needs to be combined with other nitrogen element in order to complete its octet. This combination of 2 Nitrogen atoms is called triple bond with a symbol of ( : N ≡ N: )