Final answer:
The addition of a halide to an alkene involves a halogenation reaction, where the alkene's double bond reacts with a halogen molecule or hydrogen halide to produce a disubstituted or monosubstituted alkyl halide, respectively. Intermediate species such as a halonium ion or a carbocation are formed during this process before the final alkyl halide product is obtained.
Step-by-step explanation:
The mechanism for the addition of a halide to an alkene can be described by a halogenation reaction when elemental halogen is added to an alkene to form a disubstituted alkyl halide. For instance, the addition of bromine to ethene results in 1,2-dibromoethane. In a different reaction, hydrogen halide addition to an alkene, such as the reaction of hydrogen chloride with ethene, produces a monosubstituted alkyl halide like chloroethane.
During these addition reactions, the halogen molecule or hydrogen halide interacts with the C-C double bond of the alkene. The π bond electrons act as a nucleophile, attacking the halogen to form a transient halonium ion or carbocation intermediate, which then reacts with a halide ion (in the case of elemental halogens) or hydrogen (in the case of hydrogen halides) to produce the alkyl halide product. The alkyl halides so formed can be further transformed into a variety of other organic compounds via an SN2 reaction.