FORMAL CHARGE is a concept used to determine the most probable Lewis structure. The formal charge of an atom in a Lewis formula is the hypothetical charge you obtain by assuming that bonding electrons are equally shared between bonded atoms and that the electrons of each lone pair (nonbonding pair) belong completely to one atom. Formal Charge = G – B – N.E G = Group number of the element in the periodic table. B = Number of bonds of the element in the molecule. N.E = Number of nonbonding electrons of the element in the molecule. To apply this formula, first we need the lewis structure of hypobromite ion: [:O:Br:]^- It is not shown here but there must be 2 e- above and 2 e- below each of O and Br atoms, that is complete octet. As you know Br is a halogen with 7 valence electron. It shares 1e- with O and completes its octet. On the other hand, O is in group VIA and has 6 valence electrons. After sharing 1e- with bromine now it has 7e-. The ion carries – charge because of an extra e-. Tog