Final answer:
Alkenes and alkynes are more reactive than alkanes due to pi (π) bonds present in their double and triple bonds, respectively. These pi bonds create high electron density regions, making alkenes and alkynes nucleophiles that readily react with electrophiles, through electrophilic addition reactions. Alkanes, on the other hand, lack such reactive sites due to their nonpolar single bonds.
Step-by-step explanation:
Alkenes and alkynes are more reactive than alkanes due to the presence of pi (π) bonds. In alkenes, the carbon-carbon double bond contains one σ-bond and one π-bond, while in alkynes, the carbon-carbon triple bond contains one σ-bond and two π-bonds. The π electrons are more loosely bound and occupy a region of high electron density, making these compounds nucleophiles and more susceptible to electrophilic attack.
Electrophiles, such as halogens, can react with these electron-rich regions in alkenes and alkynes. During an electrophilic addition, the π-bond electrons are used to form a new σ-bond with the electrophile, creating a carbocation intermediate which then reacts rapidly with a nucleophile. Alkynes can react with twice as much reagent since they have two π-bonds compared to one in alkenes.
In contrast, alkanes have only single C-C and C-H bonds, which are relatively nonpolar and strong, making them less reactive nucleophiles. Therefore, alkanes are generally unreactive towards electrophilic addition reactions, unlike alkenes and alkynes that are more prone to these reactions.