The halogens are the salt forming elements placed in Group 17 of the periodic table . The halogen family elements include elements Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine. These exist in the elemental form as diatomic molecules. The Group 17 gases are also called as halogen gases.

Halogens are highly reactive non–metals. At room temperature fluorine and chlorine exist as 'gas'; bromine is liquid and Iodine is a solid. The final member of the group, namely astatine, is intensely radioactive. Its most stable isotope has a half–life of only 8.3 hours. Fluorine is the most electronegative element found in nature.

Halogens have a general electronic configuration of ns²np⁵ ,Thus the addition of only one further electron by either ionic or covalent bonding will confer a noble gas configuration to the halogen atom.

They are strong oxidizing agents as they borrow electrons. The most common oxidation state for the group VII elements is −1, although other oxidation states do exist. They attain noble gas configuration either by gaining one electron to form compounds like NaCl, KI, LiF or by sharing to form a single covalent bond ( HCl, HBr, CCl₄, BF₃). As the atomic number increases the group VII elements become less reactive. They also become less volatile and darker in color. Fluorine is a pale yellow gas at room temperature, whilst chlorine is a dark greenish yellow. Bromine is a dark red liquid giving off a dense red vapor, whilst iodine is a shiny, greyish black crystalline solid, which can be sublimed to a purple vapor.

The decrease in volatility of the elements down the group is the result of increasingly strong van der Waals forces between the molecules as the relative molecular mass increases. These increased intermolecular forces also account for the observed increases in melting points, boiling points and enthalpy changes of vaporization. Because the halogens form simple, non–polar molecules, they dissolve readily in non–polar organic solvents such as tetrachloromethane. However, chlorine, bromine and iodine are sparingly soluble in water too, although chlorine also undergoes a very slow reaction with the water forming initially chloric acid, HClO(aq), which decomposes to give oxygen and hydrochloric acid:

Halogens reacts with metals forns ionic and covalent compounds and with non–metals form covalent compounds.

Uses of halogens

• In manufacture of halogen lamps.
• Fluorine as fluoride used in tooth pastes, Chlorine is used to treat waste water and sewage,Bromine compounds play an important role in the manufacture of pharmaceuticals and Iodine has been very useful in treating acne, conjunctivitis, cretinism, vaginitis and ovarian problems.

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