Answer
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Work Step by Step
Formal charge is a bookkeeping tool used to determine how electrons are distributed among the atoms in a molecule or ion. It helps identify the most stable or likely Lewis structure by showing which atoms carry positive, negative, or neutral charges. The formal charge (FC) of an atom is calculated using the formula:
FC = (valence electrons) − (nonbonding electrons)−$\frac{1}{2}$ (bonding electrons)
The purpose of calculating formal charge is to ensure that the chosen Lewis structure represents the most stable distribution of electrons—generally, the structure in which most atoms have a formal charge of zero, and any charges that remain are placed on the most appropriate atoms (negative charges on more electronegative atoms, positive charges on less electronegative ones).
In organic compounds, the main elements—C, H, N, O, and Cl—tend to form a specific number of bonds that allow them to satisfy the octet rule (or duet rule for hydrogen) and achieve a formal charge of zero. Carbon forms four bonds, hydrogen forms one, nitrogen forms three bonds and has one lone pair, oxygen forms two bonds and has two lone pairs, and chlorine forms one bond and has three lone pairs. When each of these elements forms this typical number of bonds, their formal charge equals zero, resulting in stable, neutral organic molecules that obey the octet rule.
