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Formal charge is the charge which is assigned to an atom in a molecule. To calculate formal charge you add the number of lone pair electrons to half of the number of bound electrons, and subtract the sum from the number of valence electrons.
The formal charge of an atom indicates gain or loss of electrons while forming a covalent bond. To determine formal charge, count the number of shared electrons (s), count each number of lone pair electron (L) and then follow the formula: FC (formal charge) = V (valence electrons) - (L + s/2)
Additionally, if your molecule is charged, the sums each of the formal charges of the atoms should equal the total charge of the molecule. The Lewis structure in which formal charges of individual atoms are closest to zero represents the lowest energy arrangement.
Formal charge is the charge assigned to an atom assuming the electrons are shared equally. You calculate formal charge with the equation FC = V - (L + S/2) where FC = formal charge, V = valence electrons, L = lone pair electrons, and s = shared electrons of that specific atom.
In the formula, instead of using S/2 I just count the number of bonds with that atom and you get the same answer. I think it's a little bit easier since you don't have to divide by two and can subtract that exact number.
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