Lewis Structure HClO3

[AnnikaMittelhauser4E]

Question 2C3 asks for the lewis structure of HClO3. I came up with the structure below in which I think everything has a formal charge of 0, and there are no expanded octets.

But in reality, it has an expanded octet on chlorine and resonance as its most stable structure (furthest right).

How am I supposed to know that the second structure is better? Is it just because usually the molecules we see aren't chains unless they're made of carbon? I know the expanded octet on chlorine is possible - I just thought it would be less favorable. Does the stability of the resonance make the difference?

[Tiffany_Chen 2K]

I think it has to do with HClO3 being a strong acid, thus ClO3 would be a structure, and the remaining hydrogen would be bonded to an oxygen (as H+ will dissociate in water to form H3O+, leaving ClO3-).

[Rohit Ghosh 4F]

The book also says that in all oxoacids, the hydrogen involved has to have a single bond with an oxygen.