Question

what does an -ite or -ate ending in a polyatomic ion mean? i'm thinking it mean Oxygen is in the formula, or is it Sulfur is in the formula? i'm not sure

oxygen is in both ites and ates. The ate has more oxygen than ite.
NaClO2 sodium chlorite
NaClO3 sodium chlorate
NaClO4 sodium PERchlorate (more O than ate).
NaClO sodium HYPOchlorite (less O than ite).

is this the correct name for N3-

Nitride ion

I assume that is a -3 charge as in
N^-3. Yes, it is the nitride ion. Magnesium nitride is

Mg₃N₂

thanks