Bonding molecular orbitals are created by the in-phase combination of atomic orbitals. Antibonding molecular orbitals are created by the out-of-phase combination of atomic orbitals. They hold electrons primarily away from the region between nuclei.
According to molecular orbital theory, when the orbitals from two atoms combine, one bonding orbital and one antibonding orbital are formed. The number of molecular orbitals formed will depend on the number of electrons filling the orbitals in the atoms.