Bromine (atomic symbol Br) is a liquid, nonmetal halogen. Halogens are all “salt-formers." Bromine is atomic number 35, period 4 and group 17 on the periodic table. As a liquid, Bromine is reddish-brown, heavy and very dangerous. When in vapor form it is also reddish in color, very irritating to the eyes and has a strong unpleasant odor. Despite the dangers that elemental bromine presents, it has been used since ancient times, and compounds are still in use today.
The first century Roman writer Pliny described the process used to create purple dye. The color was obtained from a marine mollusk called the murex and contained the compound 6,6’-dibromoindigo. Bromine was not prepared in any significant quantity until 1860 and was discovered and named in 1826. German chemist Justus von Leibig can almost be credited with discovering bromine in 1825 when he was sent a sample of salt spring water to analyze from Bad Kreuznach. It contained bromine, which he isolated, but he incorrectly concluded that it was a compound of chlorine and iodine, thus missing the opportunity to discover a new element.
The very same year, Carl Loewig, another German chemist, almost discovered bromine when he was still only a student at Heidelberg University. Loewig was from Bad Kreuznach. He took water from a salt spring, added chlorine and observed a red substance, but he did not research it further.
The next year, bromine was officially discovered. Antoine Balard had been studying the plants in a salt marsh in France since 1824, but became interested in the salt deposits. He completed the same process as Loewig and published his results in 1826. Bromine was then named from the Greek word “bromos,” meaning “stench.”
Elemental bromine, the dangerous form of bromine, is diatomic, appearing as Br2. It is the only nonmetal that is liquid and the only liquid halogen. It will quickly evaporate into a vapor, smelling similar to chlorine. It is less reactive than chlorine and fluorine, but more reactive than iodine. Like chlorine, it also acts as a bleaching agent. Bromine has 26 isotopes, with mass numbers ranging between 68 and 94. Naturally occurring bromine is composed almost equally of the two stable isotopes, Br-79 and Br-81.
Today bromine is mainly extracted from seawater and still used in dyes. It also has commercial uses in pesticides, water purification and to make fire-retardant plastics. Potassium bromide is used to form bromide ions, which are used to manufacture silver bromide, used in photographic film. Formerly, there was a high demand for the compound 1,2-dibromoethane (C2H4Br2). It increases the octane level of gasoline by preventing the buildup of lead in engines, but the increased use of unleaded gasoline has in turn substantially decreased the need for bromine.