Molecular Orbital Theory

                    

   Diatomic molecules: Hetero nuclear molecules

In hetero nuclear diatomic molecules, the relative contribution of atomic orbitals to each MO is not equal.  Some MO’s will have more contribution from A O’s on one atom than from A O’s on the other.  

This means that the coefficients in the MO will not be the same!  

For example, in hydrogen fluoride (HF), some orbitals are derived more from H than F and vice versa.  The more the contribution from AO’s on a given atom, the higher the coefficient in front of the AO in the MO. 

The combinations of s symmetry: (note that the 1s orbital on H is closer in energy to the 2pz orbital on F so we will look at that combination because there will be more interaction)

Because the contributions are not equal, the MO diagram will be skewed.

There is a little bit of mixing between the H 1s and the F 2s orbital but it interacts mostly with the 2pz. scc-education.com

F also has the 2px and 2py orbitals that cannot interact with the H 1s orbital because they have the wrong symmetry!  If you try to combine these orbitals with the 1s on H, you will find that the overlap integral, S, is equal to 0.  Thus these orbitals are exclusively found on the F atom and are called non-bonding.  The energies of these orbitals do not change from the energies in the F atom.

The orbitals that are derived mostly from F are going to be closer to the energies of the atomic orbitals of F and vice versa.

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