Formal charge - the difference between the number of valence electrons on free atom and number of valence electrons assigned to the atom in a molecule (valence e- shared - valence assigned)
- lone pairs belong entirely to the atom in question - shared pairs are divided equally - atoms try to achieve formal charges as close to zero as possible - negative formal charges go to the most electronegative element involved in the bond - the sum of all the formal charges on an ion or molecule equal the overall charge on the species - formal charges are only estimates - not actual charges - actual charges are determined experimentally