Explain why Lithium (Li) and Nitrogen (N) / have different amounts of valence electrons but

Lithium (Li) and Sodium (Na) have the same amount of valence electrons.

Li⁺, Na⁺ (group 1); N⁻³ (group 15)

Explanation:

Li and Na belong to group 1 of the periodic table so they coincide in the valence electrons which, being group 1, is a single electron.

They are very willing to lose it because they have little electronic affinity. In addition, both elements enter the alkali metal group (all of group 1)

They are cations, as they make ionic bonds.

N is an element from group 15. It is a nonmetal and has 5 electrons in its last layer as all the elements that make up its group, P, As, Sb so it would subtract 3 more electrons to have its last complete level and thus reach noble gas configuration.

Nitrogen can make covalent bonds, for example with O, where they form anions because it can gain electrons.