Which expression correctly defines the formal charge in the formula FC = GN - UE - 1/2 BE?

Which expression correctly defines the formal charge in the formula FC = GN - UE - 1/2 BE?

• A. FC = GN - UE - 1/2 BE
• B. FC = GN + UE - BE
• C. FC = GN - UE - BE
• D. FC = GN - 2UE - 1/2 BE

Answer: (A)

Formal charge is a bookkeeping method that tells you how many electrons an atom effectively “owns” in a molecule compared to its neutral state. You start with the number of valence electrons the atom has when neutral (its group number). From that, you subtract the electrons assigned to the atom in the Lewis structure: the nonbonding (unshared) electrons on the atom, and half of the electrons in bonds around the atom because each bond is shared between two atoms. So the correct form is FC = GN - UE - 1/2 BE, where GN is the valence electron count for the neutral atom, UE is the number of unshared electrons on the atom, and BE is the number of electrons in bonds around the atom. This reflects that lone pairs belong wholly to the atom while bonding electrons are shared, hence only half of them are assigned to the atom for formal charge purposes. Subtracting all bonding electrons or double-counting lone pairs would miscount the electrons, leading to an incorrect formal charge.

Formal charge is a bookkeeping method that tells you how many electrons an atom effectively “owns” in a molecule compared to its neutral state. You start with the number of valence electrons the atom has when neutral (its group number). From that, you subtract the electrons assigned to the atom in the Lewis structure: the nonbonding (unshared) electrons on the atom, and half of the electrons in bonds around the atom because each bond is shared between two atoms. So the correct form is FC = GN - UE - 1/2 BE, where GN is the valence electron count for the neutral atom, UE is the number of unshared electrons on the atom, and BE is the number of electrons in bonds around the atom. This reflects that lone pairs belong wholly to the atom while bonding electrons are shared, hence only half of them are assigned to the atom for formal charge purposes. Subtracting all bonding electrons or double-counting lone pairs would miscount the electrons, leading to an incorrect formal charge.