How is the bonding in alkenes different from alkanes?

Alkenes have a double bond between carbon atoms, unlike alkanes which only have single bonds.

Alkenes and alkanes are both hydrocarbons, meaning they are composed of hydrogen and carbon atoms. However, the key difference lies in the type of bonding between the carbon atoms. In alkanes, each carbon atom is connected to its neighbouring carbon atoms by a single covalent bond. This means that each carbon atom shares one pair of electrons with each of its neighbouring carbon atoms. This type of bond allows for free rotation around the bond axis, making alkanes flexible molecules.

On the other hand, alkenes contain a double bond between two of the carbon atoms. This double bond consists of a sigma bond (σ) and a pi bond (π). The sigma bond is formed by the end-to-end overlapping of atomic orbitals, while the pi bond is formed by the side-to-side overlapping. The presence of the pi bond 'locks' the atoms in place, preventing rotation around the bond axis. This gives alkenes a rigid, planar structure.

The presence of the double bond in alkenes also affects their chemical reactivity. Alkenes are more reactive than alkanes due to the presence of the pi bond, which is weaker than the sigma bond and thus more easily broken. This makes alkenes more susceptible to reactions such as addition reactions, where other atoms or molecules can add across the double bond.

In summary, the bonding in alkenes is different from alkanes in that alkenes have a double bond between carbon atoms, which gives them a rigid structure and makes them more chemically reactive.