This section is quite small it is on the reactions of a halogens- they are diatomic- meaning they come as 2 atoms and how they inter-react with each other:
Basically:

The halogen is added across the C=C double bond
Glossary: Halogens: the following elements are the halogen - F (fluorine), Cl (clorine), Br (bromine), I (iodine) and At (astatine,however hardly ever used) |