Molecular Orbital Theory Molecular Orbital (MO) Theory is a sophisticated bonding model. It is generally considered to be more powerful than Lewis and Valence Bond Theories for predicting molecular properties, however this power comes at the price of complexity. In its full development, MO Theory requires complex mathematics, though the ideas behind it are simple. Atomic orbitals (AOs) that are localized on individual atoms combine to make molecular orbitals (MOs) that are distributed over the molecule. The simplest example is the molecule, dihydrogen (H 2 ), in which two independent hydrogen 1s orbitals combine to form the sigma bonding and antibonding orbitals of the dihydrogen molecule (see figure). The MO’s are also called Linear Combinations of Atomic Orbitals (LCAO). 5.1: Formation of Molecular Orbitals from Atomic Orbitals 5.1.1: Molecular Orbitals from s Orbitals 5.1.2: Molecular Orbitals from p Orbitals 5.1.3: Molecular orbitals from d orbitals 5.1.4: Nonbonding Orbitals and Other Factors 5.2: Homonuclear Diatomic Molecules 5.2.1: Molecular Orbitals 5.2.2: Orbital Mixing 5.2.3: Diatomic Molecules of the First and Second Periods 5.2.4: Photoelectron Spectroscopy 5.3: Heteronuclear Diatomic Molecules 5.3.1: Polar bonds 5.3.2: Ionic Compounds and Molecular Orbitals 5.4: Diatomic Molecular Orbitals 5.4.1: Molecular Orbital Theory 5.P: Problems