Drawing resonance structure for SO42

[Sunwoo Bae]

Homework Statement

Draw the important resonance forms for SO42-

Relevant Equations

none

I was told that there are six resonance structures for SO42-, as shown below.

I am wondering why this structure with single bonds is not one of the possible resonance.
I understand that it is unfavorable as the formal charges are spread out over all four atoms, but shouldn't is still be a part of the resonance, given that the total formal charge of the molecule adds up to 2- in total?

Thank you

 

[mjc123]

Theoretically that is a possible resonance structure, but that degree of charge separation makes it much less stable than the other structures, so it contributes very little to the resonance hybrid.