Formal Charge:
Formal charge of an atom having more than one molecules or ions is the difference between valance electron of that atom.
Short Trick to find Formal Charge –
Number of valance electrons – (No. of unshared electrons + No. of bonds)
Example –
NH4+
Formal Charge of N = 5 – (0+4) = +1
Formal Charge of H = 1 – (0+1 ) = 0
So, Formal Charge of NH4+ = 0+1 = +1
(CO3)-2
Formal Charge of C = 4 – (0 + 4) = 0
Formal Charge of O(a) = 6 – (6+1) = -1
Formal Charge of O(b) = 6 – (6+1) = -1
Formal Charge of O(c) = 6 – (4+2) = 0
So, Formal Charge of (CO3)-2 = -2
The fact that formal charges are theoretical does not imply any actual charge separation within the molecule.
The formal charge helps to select some possible Lewis structure background resistance shapes for a given species.
Knowing the shape of the background current can easily predict most of the manufactured parts from the reaction and also describe some phenomena.
Generally, the bottom electricity shape is the only with the smallest formal charges at the atoms and the maximum dispensed charge.