A formal charge is the charge assigned to an atom in a molecule in the covalent view of bonding assuming that electrons in all chemical bonds are shared equally between atoms regardless of relative electronegativity. It is the difference between an atoms number of valence electrons in its neutral state and the number allocated to that atom in a Lewis structure. Qf=v−(V+B) where, V is sumber of valence electron in free atom. U= Number of unshared electron in atom. B= Number of bond around the atom.