I recently began learning about resonance in molecules-

I drew the following Lewis dot structure for $\ce{CO^{2-}_3}$ ion and accounted for resonance in it.

enter image description here

Now I was asked about hybridisation and bond order of $\ce{O}$ in carbonate ion.

I thought that it will definitely not be $\ce{sp^3}$ and $\ce{sp^2}$ as indicated in Lewis dot structure of it because actual structure of carbonate is hybrid of above structures.

I started by treating each oxygen $\ce{sp^2}$ hybridised. Now all of them have unhybridised $p$ orbital perpendicular to the monitor screen and their sigma bonds are accounted by $\ce{sp^2}$ orbitals. The four parallel $p-$ orbitals form the base for conjugated $\pi$ system containing 6 electrons.

But the answer to the question was two oxygen have bond order 1 and $\ce{sp^3}$ hybridisation and remaining one has bond order 2 and $\ce{sp^2}$ hybridisation which is not correct I think.

Can you please correct me if I'm wrong?

  • 2
    $\begingroup$ You are right. All oxygens are equivalent. If the answer says otherwise, it is intended for those who don't know about resonance. $\endgroup$ Jul 31 at 8:04
  • $\begingroup$ And if you dig a bit further, surprise, all these oxygens are actual sp! $\endgroup$
    – Mithoron
    Jul 31 at 11:31
  • $\begingroup$ @Mithoron I actually dig a bit further but this chem.libretexts.org/Courses/can/org/… site says it to be sp2 only $\endgroup$
    – Chemara
    Jul 31 at 13:42
  • $\begingroup$ @Mithorn I also found this answer chemistry.stackexchange.com/questions/21856/… $\endgroup$
    – Chemara
    Jul 31 at 13:52
  • $\begingroup$ Welcome to the site. Note, chemical information may be advantageously formatted using on ChemSE with mhchem. Take moment to familiarize with this. You are encouraged to use it in the body of questions, answers, and comments. Because it is something special not all web browsers understand well, do not use it in the title of questions or answers. $\endgroup$
    – Buttonwood
    Jul 31 at 17:19

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