Discuss the shape of ethylene (first member of alkenes).

In ethene molecule, each carbon atom undergoes sp² hybridisation. One sp² hybrid orbital of one carbon atom overlaps axially with one sp² hybrid orbital of the other carbon atom to form sigma (σ;) C – C bond. The other two sp² hybrid orbitals of each carbon atom overlap axially with Is orbital of the hydrogen atom to form sigma (σ;) C – H bonds. The unhybridised p-orbitals of the two carbon atoms overlap sidewise with each other to form a weak  bond, The  bond consists of two  electron clouds which lie above and below the plane of carbon and hydrogen atoms. 

Thus, ethylene molecule consists of four sigma C – H bonds, one sigma C – C bond and one ; the bond between carbon-carbon atom. The bond length of carbon-carbon double bond of ethylene is 134 pm (1.34 Å).