SO3 lewis structure

[Paree Merchant 1H]

I was looking at question 6.5 in the textbook and saw that the lewis structure in the answer key was drawn with 1 double-bonded oxygen and two single-bonded ones around S as a central atom, leaving a formal charge of -1 on those oxygens and +2 on the central Sulfur. I am confused about why this resonance structure was drawn for SO3 since wouldn't it be more stable and minimize formal charge if all 3 oxygens were double bonded?

[906430805]

It may not be a stable structure, and probably isn't the most common structure, but it is still a possible structure given the number of electrons.

There can still be other structures even if this one is listed.

[406501249]

Hi Paree,

Yes I believe you are correct in that SO3 would be most stable with 3 double-bonded oxygen atoms. However, since SO3 is a neutral molecule, the Lewis structure that the textbook provides is also correct because it has an overall charge of 0 (2(-1) + 2 = 0). Both the Lewis structures drawn with 3 double-bonded oxygen atoms and with 1 double-bonded oxygen and 2 single-bonded oxygen contain 24 e-, so there is no problem there. The only issue with the Lewis structure with 3 double-bonded oxygen atoms, is that it would give S more than an octet, which might not be allowed with other atoms, however, S is in the 3rd period and 3d orbitals are allowed to have an expanded octet. So, technically I believe both Lewis structures are correct, but I think you are right that the one with 3 double-bonded oxygen atoms would be more stable.

Great question!
Kaia H