Even though Valence Bond Theory does a better job of explaining bonding than VSEPR Theory, there are a few physical properties it cannot explain, such as magnetism. In order to appropriately address properties such as magnetism, Molecular Orbital Theory was developed.
9.7 Molecular Orbital Theory
When atomic orbitals overlap to form molecular orbitals their energies change. A Molecular Orbital Diagram is a convenient way to arrange the energies of the molecular orbitals created from the atomic orbitals so that we can appropriately populate these molecular orbitals with electrons. By properly filling the electrons in a Molecular Orbital diagram the bond order and magnetic properties of a molecule can be determined.
9.7 Molecular Orbital Diagrams