Understanding Hybridisation of Orbitals: From Carbon to Other Elements

[Azucena]

I'm struggling with the idea of hybridisation of orbitals.

Let's start with sp^2 hybridisation of carbon, so for example in graphene.
So C valence electrons ground state configuration is: 2s^2 2p^2

But am I right in saying that one of the 2s electrons is promoted to 2p, so that we have one electron in each of 2s, 2p_x, 2p_y and 2p_z ?
Now somehow we get hybridisation between the 2s and two of the 2p orbitals. So, does this "hybridisation" occur within each carbon atom individually? Or does it occur between two different atoms?

If it happens within each atom, what would happen if you brought in some other type of atoms? Would covalent bonds only be able to form between the new element atoms and the C atoms via the remaining 2p electron?

Back to hybridation in general; can you get hybridisation of orbitals both within a single atom, AND between two or more atoms?

With C we have one of the 2s electons moving to 2p to get hybridisation. Let's stay in the 2nd period of the periodic table; what happens with elements with higher atomic numbers like N, O and F? How can they hybridise?

Any help would be greatly appreciated!

 

[zhermes]

The orbital hybridization you're referring to happens within a single atom--allowing that atom to bond in particular ways. Carbon forming sp^2 orbitals is a way of explaining a trigonal planar geometry, and occurs when one s orbital hybridizes with the 2 occupied p orbitals (leaving one empty p orbital), yielding three sp^2 orbitals and one empty p orbital. This would look like 3 lobes (orbitals) arranged in a plane (120degrees between each lobe), each occupied by 2 valence electrons. Hope that helps.

 

[Azucena]

Thank you very much; that does clear up that part for me.
Can you get something similar happening with some other elements, say ones that are also in period two, but with more electrons like Oxygen, nitrogen or fluorine? I don't understand how it works when the 2p shell is more full than in Carbon.

Also, if you have something like sp^2 bonded C atoms; how does that hybridisation affect how they form bonds with other elements that could be introduced?

Thanks again for your help.

 

[zhermes]

Great questions. Let's look at Oxygen, its configuration is 2s^2 2p^4; if it hybridized to sp^2, it would have one s orbital + 2 p orbitals --> 3 sp^2 orbitals, each occupied by a pair of valence electrons (just like for carbon). But now, the remaining 2p orbital still exists, and is occupied by another pair of electrons (instead of remaining empty, as in the case of Carbon). This would look like: three planar (lets say the x-y plane) lobes (the 3 sp^2 orbitals) + a p-orbital with 2 electrons running perpendicular to the initial plane (so in this case the p-orbital would run along the z axis).
--------------
Now let's look at carbon in CH2O (formaldehyde i think). The central carbon atom will be sp^2 hybridized (like we talked about before), except its going to have its electrons distributed a little strangely. C has 4 valence electrons, in this case It would have one electron in each of the three sp^2 orbitals, and one electron in the remaining p-orbital.

Two of the sp^2 orbitals will each bond with a hydrogen (each one electron sp^2 orbital from carbon will overlap with the one electron of the hydrogen atom) effectively filling those sp^2 orbitals.
Okay, now the oxygen forms a double bond with the carbon: the remaining sp^2 orbital (with one electron from carbon) will overlap--along a line (a "sigma" bond)--with an oxygen electron, also the p-orbital of the carbon atom (with 1 electron in it) will overlap--horizontally/next-to-eachother (a "pi" bond)--with another oxygen electron; which is now a double bond (sigma+pi).

So, that's all pretty complicated but it does do a pretty good job of explaining the observed features of CH2O: its arranged in a planar triangle (trigonal planar), with a short/strong bond between carbon and oxygen (characteristic of a double bond), and also explains why its a stable configuration (with each atom completing a full valence shell).

 

[Azucena]

Thanks again, it's making lots more sense to me now!