these are formed from non-metals that share electrons. Because there are many sharing possibilities between two non-metals, the formula cannot be guessed unless we have a naming system that reveals the number of atoms involved.
-mono=1, di=2, tri=3, tetra=4, penta=5, hexa=6, hepta=7
-the only time we drop a prefix is if the mono is to appear at the beginning of the name
- -ex. N2O5 = dinitrogen pentoxide
- PCl3 = phosphorus trichloride