Hybridization of orbitals for Phosphorus in Phosphate Ion

[Conservation]

A relatively easy question regarding hybridized orbital (keep getting confused for some reason):

What is the hybridization state for the central phosphorus atom in a phosphate ion? I would presume that it would be sp3d to fulfill the expended octet/five bonds with the four oxygen atoms, but I read from a different online source that it is in fact sp3.

And, for quick check, this would mean that there are 4 sigma bonds and 1 pi bonds, right?

Thanks.

 

[DrDu]

Your question is not relatively easy. Although this is still widely taught, d-orbitals are never relevant to set up hybrid orbitals in main group elements.
The actual hybridization in phosphorous compounds is not something given, but rather a question of your own preferences.
sp3 does not seem to be a bad choice.

Maybe you have access to the following article via your library:
http://www.sciencedirect.com/science/article/pii/S1380732399800223
or
http://pubs.rsc.org/en/content/articlelanding/1997/ft/a700708f/unauth#!divAbstract
which treats somewhat similar sulphur compounds.

 

[Conservation]

I don't understand-there are five bonds in the ion. How can it be sp3?

 

[DrDu]

I don't understand-there are five bonds in the ion.

First, what makes you so sure that there are 5 bonds?
Second, there are many ways to set up 5 bonds: The bonds are highly ionic, so you can set up plenty of resonance structures with several covalent and several ionic bonds.
You are even free to chose different hybridizations in different resonance structures.