Ground State Resonance Structure

[UBDent19]

A sample DAT question asked how many ground-state resonance structures there are for NO3-. I can draw 4 structures, but the correct answer listed is 3. Why is the structure in red not valid? It still has an overall charge of -1. All resonance structures do not have to be equal energy. What do they mean by ground-state resonance structures? I can't even find the concept in my chemistry textbook.

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[CANgnome]

isn't this in KBB?

the atoms would rather have lower formal charges than higher formal charges. in your case, N has +2 when it can have fewer

 

[UBDent19]

Yes, but I've never heard of different resonance structures characterized as being in the ground state.

The question is on the sample DAT test of ADA's website. I was always taught that each valid resonance structure contributes to the true state of the molecule and the most stable forms contribute the most.

My confusion was: how would I know that the structure in red is an "non-ground state" compared to being simply the resonance structure with the highest energy, necessitating that I not include it in my answer.

 

[UBDent19]

I think I figured it out. N2+ does not have a full octet....I still can find a reference to "ground state" resonance structures in my textbook but I think I see what they mean.