In the formula for formal charge, what does GN represent?

• A. Atomic number
• B. The periodic table group number (or the number of valence electrons in a free, non-bonded atom)
• C. Number of unshared electrons
• D. The total number of electrons in the atom

Answer: (B)

GN represents the number of valence electrons the atom brings as a neutral, free atom, which is the group number on the periodic table for main-group elements. In the formal charge formula, FC = GN − (nonbonding electrons + 1/2 bonding electrons), you start with the valence electrons, not the total electrons or the atomic number. The number of unshared electrons is part of the nonbonding term, and the total number of electrons in the atom is not what GN counts. So the option describing the periodic table group number (or the valence electron count in a free atom) is the best fit. For example, oxygen is in group 16, so GN = 6; if it has two lone pairs and two bonds, FC = 6 − (4 + 1/2×4) = 0.