Question

Importance of formal charge?

Answer 1

Well, it allows us to assign electrons to a particular atom in a molecule or ion......

Explanation:

......and nitrate ion, `NO_3^-` is the goto example..... A Lewis structure shows formal charge separation:

`(O=)stackrel+N(-O^(-))_2`.....three of the four participating atoms bear a charge; the overall charge is negative because there are 2 FORMAL negative charges, yet only the one positive charge. For the parent nitric acid, quaternization of nitrogen is still evident,

`(O=)stackrel+N(-O^(-))(OH)`..... a neutral molecule as required.

We could also do the same sort of thing in reaction chemistry, to represent proton transfer in an acid-base reaction:

`NH_3 + HO(O=C)CH_3 rightleftharpoons NH_4^(+) + ""^(-)O(O=C)CH_3`

And also for sulfate ion, and sulfuric acid......

`(O=)_2S(OH)_2+2H_2Orarr(O=)_2S(-O^(-))_2 + 2H_3O^+`

Of course, in all the examples, we can distribute the charge around by resonance to show the equivalence of some of the bound atoms....