Is the O2 bond hybridized or not? "Experts" give conflicting answers....

[ForgetfulPhysicist]

TL;DR Summary

Chemistry "experts" often explain the O2 bond with a claim that it is sp2 hybridized and other molecular orbital explanations show it as non-hybridized. Somebody is taking short cuts.

Hi, while trying to teach myself about molecular orbitals I came across seemingly conflicting explanations of O2 bond. In some explanations
https://antoine.frostburg.edu/chem/senese/101/bonds/faq/explaining-o2-with-vb.shtml
the bond is clearly shown as sp2 hybridized with a sigma bond between two sp2 lobes, and a pi bond between the only non-hybridized p orbitals.

Whereas other explanations
https://en.wikipedia.org/wiki/Tripl...ygen_atom_and_dioxygen_molecule_(diagram).svg
https://en.wikipedia.org/wiki/Triplet_oxygen
show the O2 bond as a sigma bond between the two p_z orbitals, and then two 1/2 bonds between the p_x and p_y orbitals, meaning there is no sp2 hybridization.

Which is rigorously correct according to the hard core quantum mathematics? Why do the chemistry "experts" (e.g. chemistry professors) offer such conflicting explanations to undergrads and graduate students? It's a recipe for misunderstanding.

 

[Mayhem]

Professors will simplify things to make concepts more digestible to undergrads. Our general chemistry teacher told us that electron spin can be thought of "electrons spinning like ball on an axis that goes through them ... but not really". Generally, using the highest level of explanation will probably give you the most accurate picture.

 

[Borek]

Which is rigorously correct according to the hard core quantum mathematics?

Neither. To be strict, explaining bonds with orbitals being combinations of atom orbitals is only an approximation.

Even speaking of individual orbitals in the presence of multiple electrons is an approximation. Reasonably good one, approximation nonetheless.

 

[ForgetfulPhysicist]

Professors will simplify things to make concepts more digestible to undergrads. Our general chemistry teacher told us that electron spin can be thought of "electrons spinning like ball on an axis that goes through them ... but not really". Generally, using the highest level of explanation will probably give you the most accurate picture.

Thanks for the reply. It’s just sad that this situation isn’t limited to undergraduates. This misinformation is told between chemistry professors too, and also to PhD students in chemistry. It’s really a hindrance on the progress of chemistry that these stories are so far from the truth.

The gross shape of the orbitals is extremely different between the two explanations, so it’s a drastic departure from reality, at best, and must be leading people to false imaginations and wasting time.

BTW , what textbook on molecular bonding (full quantum theory) do you recommend?

 

[ForgetfulPhysicist]

Neither. To be strict, explaining bonds with orbitals being combinations of atom orbitals is only an approximation.

Even speaking of individual orbitals in the presence of multiple electrons is an approximation. Reasonably good one, approximation nonetheless.

Thanks for the response. But the problem isn’t just that neither of the above stories are exactly correct. The problem is that they are grossly different stories from each other, and therefore one of them (at least) must be grossly different from the truth. It sounds like BOTH are grossly different than the truth. And people are paying $50,000 a year to hear grossly incorrect information from chemistry professors? And spreading this misinformation around to all the other disciplines that look up to chemistry. It’s really a sad situation.

BTW , what textbook on molecular bonding (full quantum theory) do you recommend?

 

[DrDu]

The point is that the different bonding models are often not as different as it may seem and calculations with and without hybridization yield often very similar results concerning bond strength, energy and angles (where applicable).
Especially in the US, there is a tradition to explain everything assuming hybridized orbitals (which goes back to the influencial books by Linus Pauling). In other regions, hybridization is only invoqued where necessary, e.g. to explain the tetrahedral shape of methane. In the case of compounds of oxygen, this is more in line with actual calculations. In oxygen, the energetic difference between s and p orbitals is too high for hybridization.
Furthermore, while VB is easy to discuss on a qualitative basis, ab initio calculations are quite demanding, so that people who are experienced enough to do quantum chemical computations, often prefer other methods like density functional theory.
It is possible to project e.g. Multi configuration SCF wavefunctions onto VB wavefunctions. This is one of the preferred ways today to get actual VB information from QC calculations.
Anyhow, most chemists are not particularly interested in quantum chemistry. Simple bonding models often work sufficiently well to predict the outcome of experiments. So using imprecise models is pragmatism, mostly.
A nice book about ab initio calculations, which at least has some chapters on VB calculations is Quantum Chemistry by McWeeny.
Why pay 50000 $ if in other countries you can study for free?

 

[Mayhem]

Thanks for the response. But the problem isn’t just that neither of the above stories are exactly correct. The problem is that they are grossly different stories from each other, and therefore one of them (at least) must be grossly different from the truth. It sounds like BOTH are grossly different than the truth. And people are paying $50,000 a year to hear grossly incorrect information from chemistry professors? And spreading this misinformation around to all the other disciplines that look up to chemistry. It’s really a sad situation.

BTW , what textbook on molecular bonding (full quantum theory) do you recommend?

To be fair, bonding theory isn't all you're paying for. The most important skill you get at uni is the ability to apply your learning to the real world. Not something you can do at home, especially with something like chemistry.

 

[DrDu]

I had a look at the pages you were referring to:
https://antoine.frostburg.edu/chem/senese/101/bonds/faq/explaining-o2-with-vb.shtml
is blatantly nonsense.

The other two pages give explanations in terms of MO theory, not VB. But hybridization is a concept from VB theory, only.
In fact, the description of triplet oxygen by VB theory is not straight forward. The first one, who gave a correct explanation was Wheland:
https://pubs.rsc.org/en/content/articlepdf/1937/tf/tf9373301499
See also
https://www.sciencedirect.com/science/article/abs/pii/0166128091901368
https://onlinelibrary.wiley.com/doi/pdf/10.1002/jcc.20490
All these papers don't use hybridized orbitals.

 

[ForgetfulPhysicist]

Much thanks. You all are heroes.

And yes, school in Europe (or other places where tuition is lower) sounds amazing.