# If double and triple bonds are stronger than single bonds then why are unsaturated hydrocarbons less stable than saturated hydrocarbons?

I have learnt that unsaturated hydrocarbons are more reactive and less stable. However if double and triple bonds are stronger and shorter bonds than single bonds, aren't they supposed to be more stable and inert?

• Aren't you forgetting the fact that for every $\pi$-bond you break, you add two $\ce{C-H}$ $\sigma$-bonds? – Pritt Balagopal Sep 26 '17 at 4:22
• Double bonds are stronger all right, but their $\pi$-components are not. – Ivan Neretin Sep 26 '17 at 4:34
• Although they are stronger, the presence of more electron density also makes them more attractive to electrophiles – Tan Yong Boon Sep 26 '17 at 6:03

Let's take ethene for example. The $\ce{C=C}$ double bond has one sigma and one pi bond. The sigma exists because of two, sp2 hybridized orbitals overlapping head-to-head. This type of covalent bonding is very strong. But since it is only sp2, there is one p orbital leftover that was not hybridized. So, each carbon takes their left over p orbital, and forms a pi bond from the p orbitals overlapping side-to-side (the p orbitals are parallel). The unhybridized p orbitals are perpendicular to the sp2 orbitals.