The formal charge gives the charge assigned to an atom in a molecule, assuming that electrons in a chemical bond are shared equally between atoms, regardless of relative electronegativity. The formal charge of any atom in a molecule can be calculated by the following equation: FC = number of valence electrons of the atom in isolation (atom in ground state) - number of non-bonding electrons on this atom in the molecule - half the total number of electrons shared in covalent bonds with other atoms in the molecule. [source:wikipedia]