• if the species is a cation, subtract the charge of the cation from the total no. of valence electrons. • 2.Count the total no. of atoms, excluding H, in the molecule or ion. Multiply that no. by 8. • Exception: multiply the no. of H’s by 2. • This tells you how many electrons you would need if you were putting 8 electrons around all atoms without any sharing of electrons (and 2 around all H’s).