Answer
a. H2^+, H2, H2^-, H2^2-
The molecular orbital model predicts these to be stable diatomic species.
b. He2^2+, He2^+, He2
The molecular orbital model does not predict these to be stable diatomic species.
Work Step by Step
According to the molecular orbital model, the stability of diatomic molecules can be predicted based on the combination and overlap of atomic orbitals.
For H2^+, H2, H2^- and H2^2-, we can see that they have a greater number of bonding electrons than antibonding electrons, which leads to the stability of these molecules.
On the other hand, He2^2+, He2^+ and He2 have a nearly equal number of bonding and antibonding electrons, which makes them less stable compared to the hydrogen molecules.
