In: Chemistry
The double bonds are stronger and shorter than single bonds. For example, a C−C single bond has an average bond energy of 347 kJ/mole while a C=C double bond has an average bond energy of 611 kJ/mole. Use valence bond theory to explain why a double bond is not simply twice as strong as a single bond.
Bond energy of C=C is not simply double the bond energy of C-C
Explain:
C=C, here C atom is sp2 hybridized. So, it has one sigma type bond and one pi-type bond. Sigma bond is formed by face-to-face overlapping between two C-sp2 orbitals. On the other hand, pi-bonds are formed by side-wise overlapping of two C-sp2 orbitals. Now, bonds that are formed by face-to-face overlaping of orbitals are more stronger, hence requires more energy to break. Pi-bonds are weeker than sigma bonds and having less bond energy than sigma bond.
Thats why C=C (1 sigma and 1 pi bond) bond energy is not exactly double the bond energy of C-C bond.