Properties of alkenes

• Alkenes are unsaturated hydrocarbons and contain at least one carbon-to-carbon double bond in their structure. Aliphatic alkenes contain one double bond and have the general formula$C_nH_{2n}$.
• For each carbon atom of the double bond, three of the four electrons are used in three sigma bonds, one to the other carbon atom of the double bond and the other two electrons to the other atoms. This leaves one electron on each carbon atom of the double bond not involved in sigma bonds. This electron is in a p orbital. This forms a pi bond.
• A pi Bond is formed by the sideways overlap of two p orbitals one from each carbon atom of the double bond.
• The shape around each of the carbon atoms in a double bond is trigonal planar because there are three regions of electron density around each of the carbon atoms so forms a bond angle around each carbon atom of 120°.
• The pi-electron density is concentrated above and below the line joining the nuclei of the bonding atoms. The pi Bond locks the two carbon atoms in position and prevents them from rotating around the double bond.