What distinguishes alkenes from alkanes?

Alkenes are distinguished from alkanes primarily by the presence of a double bond between carbon atoms. Alkenes have at least one carbon-carbon double bond, which gives them unique chemical properties and reactivity compared to alkanes, which consist only of single bonds and are classified as saturated hydrocarbons. This double bond in alkenes allows for reactions that are not possible in alkanes, such as addition reactions where other atoms or groups can be added across the double bond.

The ability of alkenes to form these bonds is crucial in various chemical reactions, making them significant in organic chemistry and various industrial applications. This characteristic of containing a double bond is the key difference that sets alkenes apart from alkanes, which contain only single bonds throughout their structure, defining them as saturated compounds.