Why Is The Bond Length Between The Two Carbon Atoms Shorter In C2H4 Than In C2H6?
In C2H6, each carbon is bonding to four atoms – three hydrogens and one other carbon. The carbon is said to be sp3 hybridised, with one electron available in each sp3 hybrid orbital to form a bond. As it is using only one sp3 hybrid to bond to the other carbon, it forms a single bond. In C2H4 however, the carbon is sp2 hybridised with one valence electron in each hybrid orbital and the fourth one in an unchanged p orbital. It then uses two of the sp2 hybrid orbitals to bond with the hydrogens and has the remaining sp2 hydrid and the unchanged p orbital left over. These then bond with the other carbon. As each carbon atom is supplying two orbitals to the bond, it forms a double bond, which is stronger than a single bond (but NOT twice as strong). The extra bonding helps pull the two carbon atoms closer together, so the bond is shorter.
