IntroductionThe elements in the last group of the periodic table are known as inert gases. They will not have chemical reactivity. Just one group before this is the group of halogens. This group is called VII-A. They will be just one electron less than the nearest inert gases. So, these halogens are very reactive and they tend to become negatively charged ions. There are five elements in this group. They are Fluorine(F2), Chlorine (Cl2), Bromine (Br2), Iodine (I2) and Astatine (At2). Among the five elements, the last one is radioactive and very unstable and the chemistry is not much known. Hence the other four elements are only well known as Halogens.
Why they are called halogens? As for the Greek language, hal means salt and gen means to generate. These four elements are the salt formers and hence they are called halogens. None of these halogens is found in nature in their elemental form. They are found as salts only. The Fluoride ions are found in Fluorite (CaF2) and Cryolite (Na3AlF6). Chloride ions are found in rock salt (NaCl), the oceans and in water in lakes that have a high salt content. Bromide and iodide ions are found in the oceans and brine wells.
Fluorine (F2) is a known highly reactive element. It is a colourless gas and very toxic. The very inert materials like asbestos, water, and silicon will give flame in presence of this element. This will form compounds even with the inert gases. It is so reactive that it can even form compounds with Kr, Xe, and Rn, elements that were once thought to be inert. Fluorine reacts with even glass and quartz. So, we can't store this gas in containers made of these materials. Separate containers made of copper and nickel alloy will be used to store this. Fluorine reacts with even these containers also but forms a protective coating on the surface and stops the further reaction. The compounds formed with fluorine are very stable. Teflon, a very well-known insulating material, is a compound containing fluorine. Freon is a gas containing carbon dichloride and fluorine that is used these days in all types of refrigeration systems. Maximum fluorine is used in making this compound only.
Chlorine (Cl2) is also a highly toxic gas. It is pale yellow-green in colour. It is a very strong oxidizing agent. It is a commercial bleaching agent and a disinfectant. It acts as a germicide. Large quantities of chlorine are used to make many solvents like carbon tetrachloride (CCl4), chloroform (CHCl3), dichloroethylene (C2H2Cl2) are some such solvents.
Bromine (Br2) is a liquid. It is reddish-orange in colour and has an unpleasant odour. Flame retardants, fire-extinguishing agents, sedatives, antiknock agents and insecticides are made using this bromine.
Iodine (I2) is solid. This is relatively volatile and sublimes when heated. "Tincture of iodine" a very well-known disinfectant, is made by using iodine only. Some of the Iodine compounds are used as catalysts in various chemical reactions, dyes and drugs.
Halogen CompoundsHalogens are very reactive and they form different stable compounds. Some important compounds of halogens are discussed below.
Uses of Halogens
Conclusion Halogens are very well-known reactive materials and have a variety of applications. They are very toxic and some fluoride compounds are very corrosive and hazardous. They should be handled very carefully. They, especially, fluorine, is having a very vital application in many industries.