CLASS :- 11
Topic :- Formal Charge
The difference between the number of valence electron in an isolated atom and the number of of electron assign (lone pair electron and sharing electron) to that in a Lewis structures of of polyatomic Ions are molecules
Formal charge of an atom in levers structures of molecules are are polyatomic ions
= total number of valence electron in isolated atom - total number of non bonding . lone pair of electrons - ½ total number of bonding electrons
Or
F C = V - L - ½ S
V= is the number of valence electrons of the neutral atom in isolation (in its ground state)
L = is the number of nonbonding (Lone pair of electrons) valence electrons on this atom in the molecule; and
S = is the total number of electrons shared in bonds with other atoms in the molecule.
If the atom has more electron in the given molecules or ion then in the free state of atom, then it is carry negative formal charge on the other hand, if the atom has less electron in the molecules then in the neutral atom, then it is carry positive formal charge and the atom has no more or less electron in the molecules then in the free state of atom, then it is carry neutral charge
Let us considered Ozone molecules
The Central oxygen atom Marked 1
FC = V-L-½ S
= 6-2-½ (6) = + 1
The End oxygen atom Marked 2
FC = V-L-½ S
= 6-4-½ (4) = 0
The End oxygen atom Marked 3
FC = V-L-½ S
= 6-6-½ (2) = -1
Application :-
The formal charge helps in the selection of highly stable and lowest energy structures from a number of possible Lewis structures for a given polyatomic molecule or ions.
the lowest energy and maximum stability structures is the one which has lowest formal charge on the atoms of the the polyatomic ions are molecules