Question

Based on formal charges, what is the best Lewis structure for `ClO_3^-`?

Answer 1

`(O=)_2Cl-O^-`; there is a formal lone pair on the chlorine atom.

Explanation:

There are `7+3xx6+1=26" valence electrons"` to distribute over 4 centres. And given 13 electron pairs, the Lewis structure as given is reasonable. The chlorine atom bears a formal lone pair.

Since, there are 4 regions of electron density around chlorine, the structure is based on a tetrahedron, but the lone pair based on chlorine, while stereochemically active, is not considered in the structure. The negative charge on one of the oxygen atoms, may be distributed to the other oxygens, which are formally doubly bound. The structure should thus be an analogue of ammonia.