Inorganic chemistry - very general confusion

[silimay]

We have been doing a lot of d-splitting diagrams in my inorganic chemistry class.

I was wondering... I am always confused how to tell whether an orbital is a sigma orbital or a pi orbital. For instance for trigonal bipyramidal, how do you know that the two lowest are pi, the next two are pi, and the top one is sigma?

And what exactly do the stars mean?

 

[chemisttree]

The stars (asterisks) are the antibonding orbitals.


You need to know the shape of the orbitals you are combining to determine whether they are sigma or pi bonded. If the bond between the orbitals (say, from the metal to a ligand) lies along the internuclear axis, you have a sigma bond. If the bonds occur above and below the internuclear axis, the bond is a pi bond. In general pi bonds are of lower energy than sigma bonds in metal-ligand complexes.