Lewis Structure of SO2

[JennyZhu1K]

Why does one bond between S and O form a double bond while the other form a single bond. I understand that it keeps all atoms at an octahedral, but S is in the 3rd period so those extra electrons could go into the 3d orbital. Forming a double bond minimizes formal charges for both Oxygens which is what confuses me the most.

[505766240]

I think that's one way to draw the structure, but there's a resonance structure where both bonds are double bonds between S and O, making the formal charges of all atoms 0, which is favored.

[Narin Maisha 2H]

The optimal way to represent SO2 would be to have both of the bonds be double bonds. This would result in a 0 for all their formal charges which is preferred.