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sp3, sp2, sp orbitals

How do these actually ocur? I've always thought that say when C approaches H the H proton (nucleus) attracts the 2s but at the same time the C nucleus attracts it back meaning the 2s and 2p kinda 'converge', somehow :s-smilie:

. But it can't be this? Because how come on some p orbitals dont get 'converged'!

Will someone please explain. And what exactly is the difference bewteen hybridisation and the MO theory? I've tried reading about it but I just can't get it (please dumb down for me)

thanks for any replies!!!

Reply 1

Kyle_S-C

My limited understanding of it was that hybridisation doesn't actually physically occur, it's more a construction which explains the structures which arise in certain situations. I'm sure some of the more knowledgeable people on here can explain better.

Reply 2

Dhesi

The hybridisation occurs by the promotion of electrons then the mixing of orbitals. Its also to do with sigma (end on overlap occurs in sp3) and pi bonds (occurs in sp2) This link will explain in more detail http://en.wikipedia.org/wiki/Sp3 :smile:

Reply 3

hi there

Wikipedia says:

"The proton that forms the nucleus of a hydrogen atom attracts one of the valence electrons on carbon. This causes an excitation, moving a 2s electron into a 2p orbital. This, however, increases the influence of the carbon nucleus on the valence electrons by increasing the effective core potential (the amount of charge the nucleus exerts on a given electron = Charge of Core − Charge of all electrons closer to the nucleus).

The combination of these forces creates new mathematical functions known as hybridised orbitals."

So I was on the right lines. But how do sometimes you only get 1 p orbital and not the others. Surley this 'force' will have an effect on all of them?

Reply 4

-Kav-

hi there

Wikipedia says:

"The proton that forms the nucleus of a hydrogen atom attracts one of the valence electrons on carbon. This causes an excitation, moving a 2s electron into a 2p orbital. This, however, increases the influence of the carbon nucleus on the valence electrons by increasing the effective core potential (the amount of charge the nucleus exerts on a given electron = Charge of Core ? Charge of all electrons closer to the nucleus).

The combination of these forces creates new mathematical functions known as hybridised orbitals."

So I was on the right lines. But how do sometimes you only get 1 p orbital and not the others. Surley this 'force' will have an effect on all of them?

One of my lecturers wrote that. Not strictly relevant, but worth mentioning nonetheless.

Reply 5

Kyri

I'm not saying wikipedia is wrong, but I was taught in lectures that hybridisation occurs if the energy required for the promotion of the s electrons is smaller than the energy released by the forming of the additional bonds using the sp hybrid orbitals.

So you have to compare the energy gap between the s and the p orbitals of the central atom with its bond strength with whatever it is bonding to. This may be a slightly simplified way of looking at it though, as in it ignores all the maths.

Reply 6

Kyle_S-C

Well that would make sense, since chemistry is mainly about what is energetically favourable, though I still reckon that hybridisation itself is merely an approximation of extremely complicated mathematics which we can't properly understand until a fairly high level.

Hybridisation seems to occur the way it does out of necessity. In an alkene there is no other way of separating electrons sufficiently (whilst maintaining a very energetically favourable double bond) than the trigonal planar structure. This requires three symmetrical orbitals at

120^o

to one another and another out of the plane (to form the pi bond). Hence the whole VSEPR (valence shell electron pair repulsion) theory for guessing structures without any prerequisite knowledge of hybridisation.

You don't just get hybridisation randomly occurring in atoms, it's only when atoms start bonding that you get hybridisation. Once they start bonding you have to balance the energy of the electrons (empty orbitals don't have any energy) in such a way that they are in the lowest energy configuration. s < sp < sp2 < sp3 < p in energy terms, but at the same time the energy of bonding MOs is lower than some of those too. So I guess I'm pretty much agreeing with the post above.

Reply 7

charco

Study Forum Helper

1. hybridisation doesn't happen - it's just a model to explain how one situation leads to another.
2. Molecules have a different set of orbitals from atoms, although the mathematical derivation of these is very complicated (beyond even the power of modern computers) for even three centre molecules.

Taking the above into consideration, the electrons that exist in the orbitals have to be the same, so hybridisation just acts as a vehicle to explain how they might go from one organisation to another.

In reality a molecule is just an arrangement of charges in the same way as an atom. It just happens that there is more than one region of positive charge in a molecule.