Introduction:
Halogen is a chemical element that belongs to group 17 of the periodic table, also called the halogen group. The halogens include fluorine, chlorine, bromine, iodine, and astatine.

Functional Group:
A functional group is a specific group of atoms or bonds within a molecule that is responsible for its characteristic chemical reactions. These groups play a crucial role in determining the physical and chemical properties of the molecule.

Halogen as a Functional Group:
Halogen can act as a functional group when it is attached to a carbon atom in an organic molecule. In this case, it is referred to as a halogen functional group. The most common halogen functional groups are the chloro-, fluoro-, bromo-, and iodo- groups.

Properties of Halogen Functional Groups:
The properties of halogen functional groups depend on the type of halogen present in the molecule. Some common properties of halogen functional groups include:

- High electronegativity: Halogens have a high electronegativity due to their small atomic size, making them highly reactive.
- Polar nature: Halogens are polar in nature, meaning that they have a partial negative charge on the halogen atom and a partial positive charge on the carbon atom to which it is attached.
- Reactivity: Halogen functional groups are highly reactive and can undergo a range of chemical reactions, such as substitution, elimination, and addition reactions.

Examples of Halogen Functional Groups:
Some common examples of halogen functional groups include:

1. Chloromethane (CH3Cl)
2. Fluoroethane (C2H5F)
3. Bromobenzene (C6H5Br)
4. Iodoform (CHI3)

Conclusion:
In summary, halogen can act as a functional group in organic molecules when it is attached to a carbon atom. The properties and reactivity of halogen functional groups depend on the type of halogen present in the molecule. Some common examples of halogen functional groups include chloro-, fluoro-, bromo-, and iodo- groups.