Molecular orbital theory: the hydrogen molecule-ion

This chapter discusses the application of hydrogen molecule-ion in correlation with molecular orbital theory (MO theory). It clarifies that electrons do not belong to particular bonds but spread throughout the entire molecule in MO theory. Valence-bond theory provides the appropriate language widely used in modern discussions of bonding. The chapter then looks into the linear combinations of atomic orbitals while referencing the structures of molecular orbital, bonding orbital, antibonding orbital and σ orbitals. It explains that a molecular orbital in a homonuclear diatomic molecule is labelled either ‘gerade’ (g) symmetry or ‘ungerade’ (u) symmetry, which are all according to its behaviour under inversion symmetry.