Molecular orbital form when atomic orbitals with similar energies and proper symmetry spatially overlap each other.
For homonuclear molecule such as H2, N2, …e.t.c
s-orbitals combine with s-orbitals and p-orbitals combine with p-orbitals. In figure27.2 we have seen the interaction of s orbital with another s orbital.
For p- orbitals :
There are three px, py and pz orbitals. If we consider X-axis coincides with internuclear axis then for px orbitals, there will be end-on-end overlap along the bond axis as shown in figure 27.3. It forms s bonding and nonbonding orbitals.
For s bonding orbital, it is symmetric about the center of inversion and thus it is 
For s antibonding orbital, it is asymmetric about the center of inversion and thus it is  |
