[matus123]

Hello,

I am new to the forum and ran into this problem while reviewing General & Organic Chemistry material over the summer. I found that when trying to figure out the electron configuration of a molecule, it's impossible to use both hybridization and molecular orbital theory. For example, look at this diagram for the e-config of an oxygen molecule:

http://www.grandinetti.org/resources/Teaching/Chem121/Lectures/MolecularOrbitalTheory/O2.gif

It makes perfect sense if 2s and 2p are considered different energy levels, but I've tried the same approach taking hybridization into consideration and it does not work out at all. Basically if they are (almost) all in the same energy level, electrons wouldn't have gone into the "2s" sigma anti-bonding molecular orbital since that would have more energy than the pi orbitals. So the question is, are the two approaches irreparably incompatible? Or is there some deeper correlation I don't yet understand?

Thank you for reading all of my ramblings, and thanks in advance to anyone that helps me understand this.

[Corribus]

It's not entirely clear what you're asking, but from my perspective hybridization is something of an antiquated bonding model. It has some simplistic uses in organic chemistry to help explain geometries around carbon centers, but there are just too many cases where it's been shown to be wrong to be of any general usefulness. Molecular orbital theory is far more rigorous and widely applicable to chemical and spectroscopic modelling. It also fully embraces the important concepts of electron delocalization and molecular symmetry, the latter of which is absolutely crucial toward understanding molecular spectroscopy. Keep in mind that all bonding models are human constructs, and none of them are going to give perfect correlation with experimental data in all circumstances. The tricky thing is to know which models excel in which circumstances. In my view molecular orbital theory has the broadest usefulness, and when in doubt, it is the bonding model you should gravitate toward when you're trying to understand chemical structure. This is certainly the case in homo- and heteronuclear diatomic molecules.

[matus123]

Thank you for the enlightening response!

[TheOrganic]

I didn't get your questions properly, but I presume your basic question is are hybdridization theory and molecular orbital theory incompatible with each other?

This is tricky to answer. I can refer you to Jonathan Clayden's book on Organic Chemistry, where the author took the standpoint that " there is no contradiction! " . Always remember, hybridization is only a mathematical model. If you agree with hybridization theory, then it is compatible with molecular orbital theory. The molecular orbital theory speaks of the interaction of atomic orbitals to form molecular orbitals. Essentially, there is no restriction on the fact that you may first apply hybridization to get hybridized oribitals, and then make these hybrid orbitals interact via MOT approach. This is the approach taken in many books, including in Clayden's organic chemistry. There is nothing wrong with the approach if one agrees with hybridization. Hybridization speaks of atomic orbitals, molecular orbital theory speaks of interaction between AOs, regardless of the fact whether they are hybridized or not.

However, there is an if. The if is important because there are just too many evidences against hybridization theory. I refuse to accept a mathematical approach which when tried to correlate to physical evidences, contradict recklessly! If hybridization really occurred, then there would be something like sp, sp2 or sp3 emission lines. Have you ever heard of hybrid emission lines?