"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."