 The p-orbitals oriented in the z-direction (pz) can overlap end-on forming a bonding (symmetrical) σ orbital and an antibonding σ* molecular orbital.In contrast to the sigma 1s MO's, the σ 2p has some non-bonding electron density at either side of the nuclei and the σ* 2p has some electron density between the nuclei.The other two p-orbitals, py and px, can overlap side-on.