How does the double bond in alkenes affect their reactivity?

The double bond in alkenes makes them more reactive than alkanes due to the presence of a pi bond.

Alkenes are hydrocarbons that contain a carbon-carbon double bond. This double bond is composed of a sigma bond and a pi bond. The sigma bond is formed by the overlap of sp2 hybrid orbitals, while the pi bond is formed by the sideways overlap of p orbitals. The pi bond is weaker and more exposed than the sigma bond, making it more susceptible to attack by reagents. This is the primary reason why alkenes are more reactive than alkanes, which only contain single sigma bonds.

The reactivity of alkenes is demonstrated in various types of reactions. For instance, in addition reactions, a molecule adds to the carbon atoms of the double bond, breaking the pi bond and forming new sigma bonds. This is seen in the reaction of alkenes with halogens, hydrogen, water, and other substances.

Furthermore, the double bond in alkenes also allows for cis-trans isomerism. This is because there is restricted rotation around the double bond, which can lead to different spatial arrangements of the atoms or groups attached to the carbon atoms of the double bond. These different arrangements, or isomers, can have different chemical and physical properties, adding another layer to the reactivity of alkenes.

In summary, the double bond in alkenes, specifically the presence of a pi bond, significantly increases their reactivity compared to alkanes. This reactivity is showcased in various reactions, including addition reactions, and also allows for cis-trans isomerism.