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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: vanderwaals on February 01, 2017, 01:13:34 PM

Title: Resonance Structures of Sulfate Ion
Post by: vanderwaals on February 01, 2017, 01:13:34 PM

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.

Title: Re: Resonance Structures of Sulfate Ion
Post by: AWK on February 01, 2017, 02:15:50 PM

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

Title: Re: Resonance Structures of Sulfate Ion
Post by: vanderwaals on February 01, 2017, 05:21:47 PM

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

Title: Re: Resonance Structures of Sulfate Ion
Post by: AWK on February 01, 2017, 06:21:17 PM

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.

Title: Re: Resonance Structures of Sulfate Ion
Post by: vanderwaals on February 01, 2017, 06:27:10 PM

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...

Title: Re: Resonance Structures of Sulfate Ion
Post by: Babcock_Hall on February 01, 2017, 06:47:55 PM

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.

Title: Re: Resonance Structures of Sulfate Ion
Post by: vanderwaals on February 01, 2017, 07:08:53 PM

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

Title: Re: Resonance Structures of Sulfate Ion
Post by: AWK on February 01, 2017, 07:15:24 PM

Wikipedia: sulfate

Title: Re: Resonance Structures of Sulfate Ion
Post by: vanderwaals on February 01, 2017, 08:27:00 PM

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

Title: Re: Resonance Structures of Sulfate Ion
Post by: AWK on February 02, 2017, 01:41:15 AM

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)