Question

Why in hybridization even though pz orbital undergoes hybridization say in ethene molecule to form a pi bond. it is not regarded as hybrid orbital

Answer 1

In ethene, each carbon atom is Sp2-hybridized. In this way six Sp2-orbitals are generated (three for each carbon atom). One Sp2-orbital of each carbon atom by overlapping forms a sigma bond between carbon atoms. Remaining two Sp2-orbital of each atom overlap with 1s-orbital of hydrogen atom to produce four sigma bonds. P_z un-hybrid orbital of Each carbon atom by the parallel overlapping form a pi-bond between two carbon atoms. Pz orbitals are called un-hybrid orbitals because these orbitals do not take part in hybridization.