In
chemistry,
molecular orbital (
MO)
theory is a method for determining molecular structure in which
electrons are not assigned to individual
bonds between
atoms, but are treated as moving under the influence of the
nuclei in the whole molecule. The spatial and energetic properties of electrons within atoms are fixed by
quantum mechanics to form orbitals that contain these electrons. While
atomic orbitals contain electrons ascribed to a single atom, molecular orbitals, which surround a number of atoms in a molecule, contain
valence electrons between atoms. Molecular orbital theory, which was proposed in the early twentieth century, revolutionized the study of bonding by approximating the positions of bonded electrons—the molecular orbitals—as Linear Combinations of Atomic Orbitals (
LCAO). These approximations are now made by applying the
Density Functional Theory (DFT) or
Hartree–Fock (HF) models to the Schrödinger equation.