Molecular orbital theory: homonuclear diatomic molecules

This chapter looks into molecular orbital theory (MO theory) with respect to homonuclear diatomic molecules and ions. Molecular orbitals are constructed as linear combinations of all valence orbitals of the appropriate symmetry. Meanwhile, σ orbitals are constructed separately from valence s and p orbitals and π orbitals are constructed from the sideways overlap of p orbitals. The chapter notes overlap integral as a measure of the extent of orbital overlap. It considers the building-up principle as electrons occupy the available molecular orbitals to achieve the lowest total energy subject to the Pauli exclusion principle. Moreover, a technique like a photoelectron spectroscopy (PES) can probe the energies of molecular orbitals.