Diatomic molecules

This chapter evaluates diatomic molecules. Atomic orbitals of the correct symmetry on adjoining atoms interact to form a bonding combination orbital and an antibonding combination orbital. Molecular orbitals that display cylindrical symmetry when viewed along the bond axis are called σ orbitals. Atomic s-orbitals on adjoining atoms combine to form σ and σ*orbitals (the * denotes antibonding). Meanwhile, atomic p-orbitals on adjoining atoms combine by sideways overlap to form π and π*orbitals. The bond order is a number calculated by subtracting the number of antibonding electrons from the number of bonding electrons, and dividing by 2. Ultimately, molecular orbital energy level diagrams of homodiatomic molecules are symmetrical, but molecular orbital energy level diagrams of heterodiatomic molecules are asymmetric because the energy levels of the more electronegative atom are lower.