How do alkenes differ from alkanes in terms of bonding and reactivity?

How do alkenes differ from alkanes in terms of bonding and reactivity?

• A. Alkenes have at least one C=C double bond and undergo addition reactions; alkanes have only single bonds.
• B. Alkenes have only single bonds and are saturated.
• C. Alkanes contain C=C double bonds.
• D. Alkenes are always solids at room temperature.

Answer: (C)

The key idea is the bonding difference: alkenes have a carbon–carbon double bond, while alkanes have only single bonds. That double bond is made of a sigma bond plus a pi bond, and the pi bond is weaker and easily broken when reagents come in. Because the pi bond can open, alkenes readily undergo addition reactions where atoms add across the two carbons (for example, adding hydrogen, halogens, or water). Alkanes, with only single bonds, are considered saturated and are much less reactive in terms of adding across bonds; they mainly undergo substitution or combustion rather than addition reactions. So the presence of a C=C double bond in alkenes drives their higher reactivity in addition processes, whereas alkanes stay relatively inert due to their all-single-bond structure.

The key idea is the bonding difference: alkenes have a carbon–carbon double bond, while alkanes have only single bonds. That double bond is made of a sigma bond plus a pi bond, and the pi bond is weaker and easily broken when reagents come in. Because the pi bond can open, alkenes readily undergo addition reactions where atoms add across the two carbons (for example, adding hydrogen, halogens, or water). Alkanes, with only single bonds, are considered saturated and are much less reactive in terms of adding across bonds; they mainly undergo substitution or combustion rather than addition reactions. So the presence of a C=C double bond in alkenes drives their higher reactivity in addition processes, whereas alkanes stay relatively inert due to their all-single-bond structure.