Yesterday I learned about resonance structures and came across this problem.

The resonance structures are formed when there is a delocalized π electron cloud. I understand that for benzene, there are two resonance structures. For making π bonds I know that there are three main reasons:

  • The two orbitals should overlap each other.
  • There should only be one electron for each orbital.
  • The two orbitals should be in one level.

In benzene there are six $\mathrm{p}_z$ unhybridized orbitals, therefore they can share their electrons with each other (delocalize the π bond electrons). So benzene has 2 resonance structures.

But I don't understand how this works for the nitrite anion, $\ce{NO2-}$.

Resonance structures of Nitrite

In $\ce{NO2-}$ there is also π electron delocalization, so there are 2 resonance structures. Now I am going to say how I think the delocalization is happening.

When the first structure changes into the second structure, nitrogen has to make a π bond with the right side oxygen with each of the $\mathrm{p}_z$ orbitals before, but now that π bond's two electrons take to the right side oxygen, and then there are 2 electrons in the right side $\mathrm{p}_z$ orbital and no electrons in the nitrogen $\mathrm{p}_z$ orbital. But the left side oxygen (in the first structure, $\ce{O-}$) has 2 electrons in its $\mathrm{p}_z$ orbital. Then the nitrogen $\mathrm{p}_z$ and oxygen $\mathrm{p}_z$ overlap each other and make a π bond.

I have said before "There should only be one electron for each orbital." But, according to my understanding above, the π bond is made by $\mathrm{p}_z$ with 2 electrons (oxygen) and $\mathrm{p}_z$ with no electrons (nitrogen) overlapping each other.

So, is there any mistake in my imagination?

  • 1
    $\begingroup$ If you want to speak in terms of orbitals, then there is no such thing as resonance structures. $\endgroup$ Jun 27, 2017 at 14:06
  • $\begingroup$ @Osal Edit your question to correct punctuation and orthography errors. $\endgroup$
    – Mithoron
    Jun 27, 2017 at 14:11
  • $\begingroup$ According to that, is there not a connection between orbitals and resonance. When there are resonance structures then the pi electron cloud is also change every time. Electons are in orbitals. Therefore there is a connection between orbitals and resonance. $\endgroup$ Jun 27, 2017 at 14:19
  • 3
    $\begingroup$ Resonance structures are a convenience to help make Lewis structures more applicable in a general sense. However, since Lewis structures are still quite limited in terms of expressive power, this is just a stop gap. Don't try to read too much into the physical interpretation of resonance structures: they don't exist. $\endgroup$
    – Zhe
    Jun 27, 2017 at 14:40
  • 1
    $\begingroup$ Sure enough, there is a connection between orbitals and resonance, and it goes as follows: once you learn the former, you should forget the latter. $\endgroup$ Jun 27, 2017 at 14:44

1 Answer 1


Yes. I think that there is a mistake in your imagination. Nitrogen is evidently $sp^2$-hybridised in this case. Nitrogen has 5 valence electrons. Two electrons are used to make 2 $\sigma$ bonds with two hybrid orbitals. Another two electrons become the lone pair and reside also in a hybrid orbital. This leaves us with one electron in one unhybridised $p$ orbital. This $p$ orbital is then used to make the $\pi$ bond to either oxygen atom, contributing one electron to the $\pi$ bond while the oxygen atom also contributes one electron from its $p$ orbital.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.