Chemical element, a deep red, noxious liquid, and a member of the halogen elements, or Group 17 (Group VIIa) of the periodic table. Free bromine is a reddish-brown liquid with an appreciable vapour pressure at room temperature. Bromine vapour is amber in colour. Bromine 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. Like the other halogens, bromine exists as diatomic molecules in all aggregation states. A rare element, bromine is found in nature dispersed throughout Earth’s crust only in compounds as soluble and insoluble bromides. Some enrichment occurs in ocean water (65 parts per million by weight), in the Dead Sea (approximately 5 grams per litre [0.7 ounce per gallon]), in some thermal springs, and in rare insoluble silver bromide minerals (such as bromyrite, found in Mexico and Chile). Natural salt deposits and brines are the main sources of bromine and its compounds. Natural bromine is a mixture of two stable isotopes: bromine-79 (50.54 percent) and bromine-81 (49.46 percent). Of the 17 known radioactive isotopes of the element, bromine-77 has the longest half-life (57 hours).

Encyclopedia Britannica - http://www.britannica.com/EBchecked/topic/80822/bromine-Br