6A.15(b) - Lewis structure for SO2 and SO2Cl-

[Katherine Fitzgerald 1A]

We are asked to draw the lewis structure for for Cl-, SO2, and their product. In the answer manual, S02 has S bonded to the first oxygen with a double bond, but to the second oxygen with only a single bond, and then a lone pair. Why would this be the case rather than 2 double bonds, which would minimize formal charge? Similarly, for the product, the answer manual shows S double bonded to one oxygen, but single bonded to O and Cl with a lone pair. Why wouldn't S have double bonds with everything to minimize formal charge? S should have an expanded octet, so I don't see why 6 bonds should be a problem.

[Chem_Mod]

The reason there is not 2 double bonds to both oxygens is because then the sulfur would have a formal charge of -1 while both oxygens would be 0. There is only one double bond so that the sulfur has a formal charge of 0 and then the oxygen, which is more electronegative, receives the negative charge.

Remember to also count your total electrons. I believe what you are thinking is that the lone pair on the sulfur should form a double bond, but then that oxygen would have 10 electrons, which it cannot.