Now, if the basis set consists of s and p orbitals, only s and px orbitals can contribute to σ bonds on the x-axis. py and pz orbitals have zero density on the x-axis...Now, if the basis set consists of s and p orbitals, only s and px orbitals can contribute to σ bonds on the x-axis. py and pz orbitals have zero density on the x-axis and therefore cannot contribute to the σ bonds. ϕσ=csϕs+cpxϕpx+cpyϕpy+cpzϕpz