In the calculation of formal charge, the formal charge on an atom equals valence electrons minus which quantity?

• A. Formal charge
• B. Oxidation state
• C. Bond order
• D. Lone-pair electrons plus covalent bonds

Answer: (D)

The quantity subtracted in formal charge is the sum of the nonbonding (lone-pair) electrons and half of the electrons involved in bonds. In symbols, FC = V − (L + 1/2 B). This reflects that electrons in a covalent bond are shared, so each atom is assigned half of those bonding electrons when counting its own electrons for formal charge.

Seeing it with an example helps: in a water molecule, the oxygen atom has valence electrons V = 6. It holds two lone pairs, giving L = 4 nonbonding electrons. It forms two O–H bonds, so B = 4 bonding electrons. The formal charge on oxygen is 6 − (4 + 4/2) = 6 − (4 + 2) = 0. This shows why you don’t subtract all bonding electrons (that would give an incorrect value) and why oxidation state or bond order aren’t used in this calculation.

So, the proper quantity to subtract is the lone-pair electrons plus half of the bonding electrons, not the full bonding electrons or other unrelated quantities.