Alkenes are a homologous series of unsaturated hydrocarbons. We can identify them by the ‘ene’ at the end of their name, such as ethene. All alkenes have carbon-to-carbon double bonds, which are represented as C=C.
The general formula for alkenes is:
Due to the presence of a double bond, alkenes are generally more reactive than alkanes, which only have single bonds between carbon atoms. This double bond is the functional group of alkenes and it determines the chemical properties of alkenes.
Let’s look at the molecular formulae and structures of the first two alkenes:
|Alkene||No. of carbon atoms||Molecular formula||Structural formula||Ball + stick diagram.|
As the number of carbon atoms in an alkene molecule increases, its physical properties, such as boiling points, gradually change.
Compared to their corresponding alkanes, alkenes have two fewer hydrogen atoms, making them unsaturated. The double bond between the carbon atoms can open up to form another single bond. Therefore, each carbon atom can form four single bonds instead of one double bond and two single bonds.
This difference in bonding makes alkenes more reactive than alkanes.