[ohmyjapan16]

Hey guys. We started learning about orbital hybridisation and the molecular orbital theory and such several days ago. Sure, I can figure out some structures hybridization, but some I can't. I think it's because I don't get the how or why some "p" level orbitals remain unchanged in hybrids such as "sp" and "sp2" (sorry don't know how to do subscripts), and then moving on to the theoretical hybridization of phosphate, which would be "sp2d." By the point where I'm trying to figure out what the hybridization of phosphate is, I'm completely lost. If you guys can help explain this, that would be great. I looked at the power-point of constructing Lewis Diagrams and I still don't really get the promotion of electrons or why "p" level orbitals remain unchanged. This might be the roadblock I need to get past in order to further understand. Or maybe it's the sigma + pi bonds I'm not quite getting. Any help or suggestions would be greatly appreciated. Thanks.

[mike]

I am not sure that entirely understand your question. However, hybridised orbitals will only make single bonds, you then require the p orbitals to form multiple bonds.

[Mitch]

sp₂ means you took 1 s ormbital and 2 p orbitals to construct the hybrid orbital, thus leaving a p-orbital that was not touched or hybridized.

[tamim83]

Well, hybrid orbitals come from different orbitals mixing together.  So  sp³ hybrid orbitals are a mix of 1 s and three p orbitals (for a total of four).  I am unsure what you really want to know, but I think phosphate (PO₄^3-) would be sp3 hybridized since you need four bonds.  I saw a table in a general chemistry book that tells you how many electron groups are around the central atom, the hybridiztion and the molecular geometry so you may want to check your book, that would be a lot of help to you. 

As far as sigma and pi bonds go, sigma bonds occur when the electrons are between the bonding atoms or if the atomic orbitals are poining directly at eachother.  Pi bonds happen when the electron sor orbitals are above and below the bonding atoms  Sigma bonds therfore have electron density concentrated in a cylinder around the bonding axis btween the two atomsand pi bonds have electron density above and below the bond axis between the two atoms. 

Hope this helps some