(SO3)2- Lewis Structure Formal Charge

[Edgar Khachatryan 3G]

Hi.

The Lewis Structure for sulfite has 3 resonance structures in which the Sulfur has a formal charge of 0 and two of the oxygens have a formal charge of -1.

Why couldn't there be a 3 double bonds instead? Wouldn't this contribute to Sulfur having a formal charge of -2 and the oxygens having a formal charge of 0?

What makes the former preferable over the latter?

Thank you!

[Chem_Mod]

It is best to minimize formal charges on the central atom. Remember it is supposed to be an atom of low electronegativity (low ionization energy). Thus, a formal charge of -2 on a central sulfur atom is unfavorable.