Formal charge (FC) is an electron-bookkeeping device that gives the charge on a bonded atom in a Lewis structure relative to a nonbonded atom of the same element.
This is equal to the number electrons owned by a non-bonded atom (V) minus the number of electrons owned by a bonded atom, assuming electron pairs are shared in all bonds (NB + ½B).
To calculate formal charge compare the number of electrons "owned" by a bonded atom to the number owned by the corresponding nonbonded atom. Assume in your count that
Note that the sum of the formal charges on the atoms equals the overall charge on the ion.
This is equal to the number electrons owned by a non-bonded atom (V) minus the number of electrons owned by a bonded atom, assuming electron pairs are shared in all bonds (NB + ½B).
To calculate formal charge compare the number of electrons "owned" by a bonded atom to the number owned by the corresponding nonbonded atom. Assume in your count that
- nonbonding electrons at the atom are "owned" by that atom
- bonding electrons are equally shared. Each bonded atom owns one electron of each bond.
 NO3– | At N in NO3– 4 bonding = 4 Nonbonded N (Group ) has 5 Formal charge at N = +1 at -O in NO3– 6 nonbonding 1 bonding = 7 Nonbonded O (Group ) has 6 Formal charge at -O = -1 at =O at -O in NO3– 2 bonding 4 nonbonding = 6 Formal charge at =O = 0 |
Note that the sum of the formal charges on the atoms equals the overall charge on the ion.