Bromine

Bromine, symbol Br, poisonous element that at room temperature is a dark, reddish-brown liquid. In group 17 (or VIIa) of the periodic table, bromine is one of the halogens. The atomic number of bromine is 35.

Bromine is widely distributed in nature. It melts at -7.25° C (18.95° F), boils at 58.78° C (137.8° F), and has a relative density of 3.10; the atomic weight of the element is 79.90. Bromine is so similar in its chemical properties to chlorine, with which it is almost invariably associated, that it was not recognized as a separate element until 1826, when it was discovered and isolated by the French chemist Antoine Jérôme Balard.

At room temperature, bromine is an extremely volatile liquid, giving off a poisonous, suffocating, reddish vapour composed of diatomic molecules. If the liquid comes in contact with the skin, it causes sores that heal very slowly. Bromine is slightly soluble in water, 100 parts water dissolving about 4 parts bromine when cold or 3 parts when hot; at temperatures below 7° C (44° F) it forms, with water, a solid, reddish hydrate, Br₂·10H₂O. In the presence of alkalis, bromine reacts chemically with water to yield a mixture of hydrobromic acid (HBr), and hypobromous acid (HOBr). Bromine is very soluble in a wide variety of organic solvents, such as alcohol, ether, trichloromethane (chloroform), and carbon disulphide. It reacts chemically with many compounds and metallic elements and is slightly less active than chlorine.

Bromine does not occur in nature as a free element, but is found in bromide compounds. It was formerly a by-product of the production of common salt or of potassium from brines rich in bromides. Elemental bromine can be prepared from bromides by treatment with manganese dioxide or sodium chlorate. Increasing demand has led to the production of bromine from seawater, which contains on the average 65 parts of bromine per million.

Bromine has been used in the preparation of certain dyes and of dibromoethane (ethylene bromide), a constituent of antiknock fluid for leaded petrol. Bromides are also used in photographic compounds and in natural gas and oil production.