Formal charge in (S2CO)2-

[Nicole Shak 1L]

One of the questions in my discussion last week said to draw resonance structures where appropriate and to label formal charges, and to rank resonance structures in order of importance to overall structure.
For [S2CO]2-, the answer says that the best way to draw the structure is to put a formal charge of -1 on S and O that are single bonded, instead of putting the formal charge on both S's. I thought that the formal charge should be placed on the atom with the lower electronegativity, which I thought would be S?

[Beverly Shih 1K]

I think you're right, that it would be preferable (lower energy) to put the formal charges of -1 both on sulfur atoms, instead of one on sulfur and one on oxygen. I think that's why there's a > sign pointing towards the structure with the formal charges on sulfur--it means that structure is preferred over the other two?

[Lenaschelzig1C]

I agree. I think that by placing both charges on the sulfer atoms, you get a more stable structure.

[Bianca Nguyen 1B]

I thought putting a negative formal charge on more electronegative atoms made sense, since they’re pulling electrons toward them. In this case, I think that the answer key is right. O is more electronegative than S, so there should be a -1 charge on the O and a -1 charge on the S rather than a -1 charge on both S atoms.