The word halogen means 'salt former', and compounds that contain halogens are called salts. The halogens are diatomic, monovalent elements from Group VII of the periodic table, comprising of fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At. The halogens are the only group in the periodic table that contain elements in the three common states of matter at standard temperature and pressure.


Halogens and their compounds are very important in the chemical industry. They are used in a wide range of production including the manufacturing of chlorofluorocarbons, disinfectants, halogen lamps, oxidants, Teflon and some hydrocarbons.

Large amounts of fluorine and chlorine are consumed each year to make chlorofluorocarbons (freons) such as dichlorodifluoromethane CCl2F2 which are used as propellants in aerosols and coolants in refrigerators and air conditions.

These group VII elements and their compounds like chlorine dioxide and iodine tincture, a solution of iodine in ethanol, are used as disinfectants, providing quick solutions to germs and dirt. Large quantities of chlorine are also used each year to make solvents such as chloromethane (CH3Cl) used in dry cleaning.

Fluorine is a very strong oxidizing agent and so is chlorine; hypochlorites are used in domestic bleaches and potassium chlorate (V) is used as an oxidant in fireworks and matches. Chlorine dioxide is used to bleach wood pulp for making paper, as it whitens the paper without weakening it.

Covalently bound carbon-fluorine compounds are known as fluorocarbons. These substances are very inert. Teflon, polytetrafluoroethene, the most resistant material important in industry is a fluorocarbon polymer (CF2–CF2)n.

It has very good thermo stability and it is not wet by water and oils. It is therefore used as a coating material for linings pots, pans and gaskets that are inert to chemical reactions. It has one of the lowest coefficients of friction against any surface and when used reduces friction, wear and energy consumption of the machine. Due to the strength of the carbon-fluorine bond, it is not very reactive and so is used in cases for corrosive chemicals.

Certain metallic and non metallic halides such as Aluminium chloride are essential in effecting changes in hydrocarbons alone such as in cracking or polymerization of unsaturated hydrocarbons and polymerization together with condensation of the hydrocarbons. Small quantities of the gaseous form of these elements are used in the production of halogen lamps which are more efficient and which last longer than other lamps.

Aluminium Chloride Dimer The Aluminium Chloride Lattice

Bromine is used to prepare hydraulic fluids, flame retardants such as HBCD, hexabromocyclododecane, hair waving preparation formula, antiknock agents for petrol such as 1, 2-dibromoethane, and in the extraction of gold.

Iodine is used in the production of drugs, and dyes. Its compound silver iodide (AgI) plays an important role in photography and in attempts to induce rain by cloud seeding. Iodide is also added in salt to protect against goitre, an iodine deficiency disease characterized by a swelling of the thyroid gland and also Fluorine is incorporated into toothpaste to hinder tooth decay.


Apart from their industrial importance, halogens and their compounds also have their significances to the environment. The halogens form organic compounds best known for their industrial impact such as CFCs, PVC, PCB and DDT. However, some of these compounds are damaging to the environment.

Chlorofluorocarbons are known from studies conducted in the 1970s to be dangerous to the molecules of ozone which protect the earth from the harmful Ultraviolet (UV-B) rays of the sun. This has secondary effects including increased incidence of skin cancer and cataracts, damage to terrestrial and aquatic plant life, damage to immune systems, premature aging of the skin, increased formation of ground-level ozone (smog), and weathering of plastics.

The insecticide DDT, dichlorodiphenyltrichloroethane, is effective but damaging to the environment. The compound is hydrophobic and is absorbed by the soil; having a soil half-life of 22-30 years. From research, a strong positive correlation was discovered between death of organisms especially cats, thinning of eggshells and the use of DDT. It has been proven to be toxic and has been banned in most countries.

Plastic polymers such as polyvinyl chloride (PVC) are not biodegradable and constitute a nuisance as they continue to pile up and may trap small animals. Fires outbreaks can cause the production of corrosive products such as HCl and HF as well as poisons like halogenated dioxins and furans from these plastics and other halogen compounds.

Polychlorinated biphenyl (PCB) which is used as a dielectric fluid in transformers and capacitors and also as a coolant has been linked to liver damage and lower weights of newly born babies.

Bromine flame retardant originally used in clothing was shown to be nephrotoxic and a mutagenic. On the other hand, fire retardants reduce fire outbreaks, saving peoples lives and reducing damages to the environment.


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