Bonding in an alkene
Alkenes are unsaturated hydrocarbons. They contain a carbon-carbon double bond and have the general formula .
A C=C double bond is made from one sigma () bond and one pi () bond.
In ethene, each carbon is involved in three bonds: two C–H bonds and one C–C bond. The remaining outer electron on each carbon occupies a p orbital.
- The C–C bond results from end-on orbital overlap along the line connecting the two carbon nuclei.
- The p orbitals on the adjacent carbon atoms are parallel to one another.
- Side-on overlap of these p orbitals produces the bond.
- The bond contains one shared pair of electrons, with electron density in regions above and below the plane of the bonded atoms.
Exam Tip: If asked to explain bonding in the C=C group, identify the double bond as one bond plus one bond, and explain that the bond forms by sideways overlap of parallel p orbitals.