The hybridization of P in phosphate

[Compaq]

My query is concerning the hybridization of P in Phosphate (PO₄^3-)

I'd like to draw the Lewis dot structure here, but I'm not sure if that's possible. So I drew up some things on my whiteboard, and took a few pictures, there's all the info you need.

Look at the left image first, thank you :)

So, to summarise (look at images first), is it correct to say that the P in phosphate is sp³d hybridized, the way I argued on the board?

It's just, last year me and an other chemistry student came across this problem, and we weren't able to explain how P could have so many e- in bonding. But, recently we had a lecture on hybridization and related stuff. The sp³d hybridization allows P to have 10 e^- around itself, exactly the same way as in PCl₅

I just want to know, and now I think I do :)


Regards
Chemistry Student :)
-Compaq

 

[DrDu]

3[/SUP]d hybridized, the way I argued on the board?

It is never correct to assume d-orbitals contributing to hybrids in main group compounds. This is known for - I would guess - at least 40 years now. The d-orbitals are both energetically too high and too diffuse for hybridization in main group compounds. In cases like PCl_5 you have to use either resonance structures or equivalently non-orthogonal hybrid orbitals.
See, e.g. http://dx.doi.org/10.1016/S1380-7323(99)80022-3

 

[Compaq]

The double bond is one sigma bond and one pi bond. Only p orbitals can form pi bonds. P in phosphate still have 10 electrons, 8 of which are involved in sigma bonds, two of which involved in the pi bond.

If P is sp³ hybridized, then how do we explain that there are 10 electrons around P? There will be two electron that aren't accounted for? Or am I being stupid? The oxygen atom involved in the double bond is sp² hybridized. One electron of one of the hybridized 2p orbital forms the pi bond with one of the hybridized 3p orbital of P.

Can someone please explain the whole hybridization process? Perhaps this is above a general chemistry course, but as I'm studying chemistry I want to know :)

-Compaq

 

[DrDu]

The double bond is one sigma bond and one pi bond.

Sigma/Pi separation is an approximation for planar molecules in molecular orbital theory. In valence bond theory (=taking electron correlation into account) it does not hold.

If P is sp³ hybridized, then how do we explain that there are 10 electrons around P? There will be two electron that aren't accounted for?
-Compaq

You can start from P^+ (having 4 valence electrons) and 4 O^- (having 1 valence electron). The bonds in PO_4^3- are all equal and have a highly ionic character.

A more modern description of bonding in main group elements is:

Quantum Chemical Methods in Main-Group Chemistry
T. M. Klapötke and A. Schulz with an invited chapter by R. D. Harcourt
J. Wiley, Chichester, 1998

Klapoetke has also written a very good book on general main group chemistry, however, I think it is only available in German.