Why does ClO3- only have 2 double bonds instead of 3?

Question

I drew a Lewis Structure of ClO₃^- with 3 double bonds instead of 2 and 1 single bond but I'm wondering if it is a valid structure.  Is there a maximum amount of double bonds that Cl can make?

Answer 1

Formally yes, you could. Provided you do your electron bookkeeping and not lose any electrons anywhere, you can calculate that this would put a negative charge on Cl. Although it is formally ok, it is more logical to have a negative charge on the oxygen due to the higher electronegativity. There are also molecular orbital considerations to keep in mind, but we don't really need to go there for your purposes here.