This reaction results in addition of halogen across the double bond. It only occurs with Chlorine (Cl2) and Bromine (Br2).

Iodine does not react with many alkenes. Fluorine is too reactive, causing an explosive reaction with alkenes producing hydrogen fluoride and carbon.

In aqueous conditions, we can form halohydrins. In these, the groups added across the double bond are an OH group and one halogen atom.