The remaining two 2p orbitals on each atom, which have a nodal plane through the z-axis overlap to give π orbitals (Fig. 3.16). Bonding and antibonding π orbitals can be formed from the mutual overlap of the two 2px orbitals and, also, from the mutual overlap of the two 2py orbitals. This pattern of overlap gives rise to the two pairs of doubly degenerate energy levels shown in Fig. 3.14