Calculate the FC of an atom in a Lewis structure.

The perfect FC for an atom is 0. This is not always achievable.

An OK FC for an atom is +1/-1, but 0 is preferable.

An FC of +2/-2 is not so good, most often it might be that a better configuration should be found for that atom if this is the value of the FC.

An FC of +3/-3 is horrible, and should probably be corrected.

The arrangements in red below are not favorable to stable Lewis structures.