Formal charge

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Formal charges in ozone and the nitrate anion

In chemistry, a formal charge (FC) is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity.^[1] When determining the best Lewis structure (or predominant resonance structure) for a molecule, the structure is chosen such that the formal charge on each of the atoms is as close to zero as possible.

The formal charge of any atom in a molecule can be calculated by the following equation:

${\displaystyle FC=V-N-{\frac {B}{2}}\ }$

where V is the number of valence electrons of the neutral atom in isolation (in its ground state); N is the number of non-bonding valence electrons on this atom in the molecule; and B is the total number of electrons shared in bonds with other atoms in the molecule.

Reference: https://en.wikipedia.org/wiki/Formal_charge