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I am doing a multiple choice question for which one of the possible answers is, for the Lewis structure of NO3- (one of the oxygens is double bonded to the nitrogen and the other two are single bonded),

"one of the N-O bonds is shorter than the other two".

Apparently this is not the right answer, but my understanding was that a double bond is shorter than a single bond. I just googled it and I'm reading that the more bonds there are the shorter the bond length. So shouldn't that answer be correct?



marked as duplicate by Mithoron, Jon Custer, Todd Minehardt, A.K., Gaurang Tandon Dec 3 '18 at 3:24

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  • 2
    $\begingroup$ Resonance, resonance... all three bonds are equal. $\endgroup$ – orthocresol Dec 1 '18 at 21:37
  • $\begingroup$ Could you explain that? Is it just that the "double bond" moves around equally around the N? $\endgroup$ – M Do Dec 1 '18 at 21:39
  • $\begingroup$ It's not really a duplicate (IMO), but it contains the answer to this question nevertheless. $\endgroup$ – Martin - マーチン Dec 2 '18 at 20:11

The main reason for your answer being wrong is the phenomenon of resonance in nitrate ion dur to presence of a conjugated system. The resonance is shown in the figure below. Dur to resonance none of the cannonical structures explain the bond length in nitrate except the resonance hybrid ( which happens to be the last drawn structure). Due to resonance all bond lengths would be the same enter image description here


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