Which of the following statements about the molecular orbitals for a diatomic molecule with 2s and 2p orbitals is or are true?

Question

Which of the following statements about the molecular orbitals for a diatomic molecule with 2s and 2p orbitals is or are true?

I. The σ*_2p molecular orbital is higher in energy than a π*_2p molecular orbital because the overlap is greater for two 2p orbitals that point directly at one another.

II. The molecule has one σ_2p molecular orbital and one π_2p molecular orbital.

III. The σ_2p and π_2p molecular orbitals both have a lower energy than the 2p orbitals from which they were constructed.

Answer 1

I. Two orbitals interacting in a σ fashion will always produce a greater overlap (and thus a greater energy change) than those same two orbitals overlapping in a π arrangement. This statement is TRUE.

II. Each individual atom will contribute 3 p-orbitals to the molecular bond; one set of p-orbitals will interact end-to-end (a σ-bond), but the remaining 2 sets of p-orbitals will both interact in a side-on arrangement (a π bond). Therefore, this statement is FALSE, as there must be two π_2p molecular orbitals.

III. The bonding molecular orbitals will always be lower in energy than the atomic orbitals that make them thanks to the constructive interference between the two wavefunctions (also, keep in mind that bond formation is always an exothermic process). Thus, this statement is TRUE.

I hope this helped!