[vanderwaals]

I'm confused about this question that asks which resonance structure of the sulfate ion contributes most to the electronic structure of the sulfate ion (the answer choices are in the attached picture). The correct answer is A, but I don't understand why it's not C. All the atoms in C have a formal charge of 0, which is more favorable than the formal charges on A. Does the answer have to do with the expanded octet on C? Thanks in advance for your help.

[AWK]

All S-O bonds in crystal structure of sulfates are the same. What does it mean?

[vanderwaals]

Doesn't that just mean there's resonance in the sulfate ion?

[AWK]

Only your structure A shows all electrons. Choose from other structures that one  with only  two minus charges ( and null charge on sulfur), draw all(!) electrons and all equivalence forms for it.

[vanderwaals]

I got this problem from a multiple choice set that didn't draw out all the lone pairs in the oxygens (which really annoys me), so I don't have much of a choice but to choose from the available choices...

[Babcock_Hall]

Some authors suggest that expanded octets are less important contributors to the overall structure than previously thought.  I recall seeing an article in J. Chem. Ed. on this subject some time ago.

[vanderwaals]

Thanks for the response. Does that mean that resonance structures without expanded octets usually contribute more than ones with expanded octets?

[AWK]

Wikipedia: sulfate

[vanderwaals]

Wikipedia somewhat clears things up...thanks!! Is it usually true that resonance structures with expanded octets are less favorable in real life?

[AWK]

Your structure A shows strictly octet at sulfur atom but many splitted charges.
Your structure C shows 12 electrons around S without no splitted charges. And this is the best - with other mesomeric structures (all 6 - showed in wikipedia)