[chrisso80b]

Hi all (first post)!
Im having some trouble understanding heteronuclear and polynuclear molecular orbitals, I think I pretty much understand the homonuclear molecular orbitals its just I cant get to grips with the other two. I dont understand how you actually construct them (or if you do) and what all the double/ triple lines mean in the diagrams (I know they mean degenerate orbitals but how do you know the molecular actually contains them???) Basically what im asking is, is it actually possible to construct a hetero/ polynuclear molecular orbital diagram from scratch, including all the letter/ subscripts/ superscripts etc.
Thanks in advanced
(Feel free to ask if you have any questions- im not great at explaining things )

[tamim83]

I am assuming your asking about heteronuclear diatomic MOs.  You can generate them the same way you do for the homonuclear diatomic MOs but the atomic orbitals for the more electronegative atom are lower in energy.  This means that the M0s themselves look a little different.  There is more electron density on the more electronegative atom if the orbital is bonding and less electron density if the orbital is antibonding.  So the orbitals look a bit "lopsided". 

MOs for polynuclear molecules can get much more difficult to generate, you need group theory to help you.  If the molecule is really large, it's just easier to plug it into the computer.  I can come up with MOs for 3 and 4 atom molecules (like ammonia or water) by hand. 

[chrisso80b]

I get that bit but how can you tell which orbitals are degenerate and which orbitals will 'combine'?
Thanks