Bromine is a chemical element with symbol Br and atomic number 35. It is the third-lightest halogen, a deep red, noxious liquid, and a member of the halogen elements, or Group 17 (Group VIIa) of the periodic table. Elemental bromine is very reactive and thus does not occur free in nature, but in colourless soluble crystalline mineral halide salts, analogous to table salt. Commercially the element is easily extracted from brine pools, mostly in the United States, Israel and China. The mass of bromine in the oceans is about one three-hundredth that of chlorine. Because of the bad odour of the element, the French Academy of Sciences suggested the name bromine, from the Greek word bromos, meaning “bad smell” or “stench”.
It was discovered in 1826 by the French chemist Antoine-Jérôme Balard in the residues from the manufacture of sea salt at Montpellier. He liberated the element by passing chlorine through an aqueous solution of the residues, which contained magnesium bromide. Distillation of the material with manganese dioxide and sulfuric acid produced red vapours, which condensed to a dark liquid. The similarity of this procedure to that for making chlorine suggested to Balard that he had obtained a new element similar to chlorine.
Characteristics of Bromine
- Free Br is a reddish brown liquid with an appreciable vapour pressure at room temperature. Bromine vapour is amber in colour.
- It has a pungent odour and is irritating to the skin, eyes, and respiratory system. Exposure to concentrated bromine vapour, even for a short time, may be fatal. It exists as diatomic molecules in all aggregation states.
- About 3.41 grams of Br dissolve in 100 millilitres of water at room temperature. The solution is known as bromine water.
- The electron affinity of bromine is high and is similar to that of chlorine. It is, however, a less powerful oxidizing agent, chiefly because of the weaker hydration of the bromide ion as compared with the chloride ion.
- An organic bromo compound resembles the corresponding chloro derivative but is usually more dense, less volatile, less combustible, and less stable.