Molecular orbital

"Molecular orbital (MO) theory describes covalent bond formation as arising from a mathematical combination of atomic orbitals (wave functions) on different atoms to form molecular orbitals, so called because they belong to the entire molecule rather than to an individual atom. Just as an atomic orbital, whether unhybridized or hybridized, describes a region of space around an atom where an electron is likely to be found, so a molecular orbital describes a region of space in a molecule where electrons are most likely to be found."

"How do we construct H2 by using atomic orbitals? An answer to this question was developed by Pauling: Bonds are made by the in-phase overlap of atomic orbitals... The in-phase overlap of the two 1s orbitals results in a new orbital of lower energy called a bonding molecular orbital... On the other hand, out-of-phase overlap between the same two atomic orbitals results in a destabilizing interaction and formation of an antibonding molecular orbital."