Final answer:
In an addition reaction between an alkene and a hydrogen halide (HBr, HCl, or HI), an alkyl halide is formed by adding a hydrogen atom to one of the carbon atoms in the double bond and a halide ion to the other.
Step-by-step explanation:
When an alkene reacts with a hydrogen halide such as HBr, HCl, or HI, the reaction that takes place is an addition reaction. This resuls in the formation of an alkyl halide. The general form of this reaction is:
R-CH=CH2 + HX → R-CH2-CH2-X
Where R is an alkyl group, and X is the halogen from the hydrogen halide (X = Br, Cl, or I). For example, if ethene (CH2=CH2) reacts with HBr, the reaction would be:
CH2=CH2 + HBr → CH3CH2Br
This reaction involves the addition of a hydrogen atom to one carbon of the double bond and a bromide ion to the other, yielding bromethane as the product. The same pattern follows with other hydrogen halides like HCl and HI.