Any electron
that occupies that molecular orbital, therefore, is attracted to both nuclei and
so has a lower energy than when it is confined to an atomic orbital on one atom.
Moreover, because the electron now occupies a greater volume than when it is confined
to a single atom, it also has a lower kinetic energy, just like a particle confined
to a bigger box (Section 1.7). A combination of atomic orbitals that results in an
overall lowering of energy, like that in Eq. 1, is called a bonding orbital.