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.

 

[quicknote]

Inorganic chemistry can be a complex subject, and it is common to have confusion about certain concepts, such as d-splitting diagrams. In terms of determining whether an orbital is a sigma or pi orbital, it is important to understand the geometric arrangement of the orbitals. In trigonal bipyramidal geometry, there are five d orbitals that are split into two sets - one set of three orbitals that lie in the same plane as the trigonal bipyramidal structure, and another set of two orbitals that are perpendicular to the plane. The three orbitals in the plane are pi orbitals, while the two perpendicular orbitals are sigma orbitals. This is because the pi orbitals have a nodal plane that contains the central atom, while the sigma orbitals do not.

As for the stars in the d-splitting diagrams, they represent the energy levels of the d orbitals. The lower the star, the lower the energy of the orbital. So in the case of trigonal bipyramidal geometry, the two lowest stars represent the pi orbitals, the next two represent the next set of pi orbitals, and the top star represents the sigma orbital.

I hope this helps clarify your confusion about d-splitting diagrams and the difference between sigma and pi orbitals. It is important to continue practicing and studying these concepts to gain a better understanding.