Bromine (Br)
Bromine (Br), with an atomic number of 35, is a halogen element that is unique as the only nonmetallic substance that is liquid at room temperature. It is characterized by its deep red color and has two naturally occurring isotopes: bromine-79 and bromine-81. Bromine is found in various environments, particularly in the oceans and inland evaporitic lakes, and is predominantly extracted from brine wells, especially in the United States, which is a leading producer. The primary applications of bromine include its use in flame retardants, which constitute about 45% of its production, as well as in agriculture, water treatment, and various chemical compounds for pharmaceuticals and dyes.
Historically, bromine was first identified as an element in 1826 by Antoine-Jérôme Balard, who derived its name from the Greek word for "bad odor." Despite concerns regarding its environmental impact, including its role in ozone depletion, bromine is essential in various industries due to its reactive nature. The methods for obtaining bromine typically involve processes that extract it from brine or seawater, often requiring complex chemical reactions. Overall, bromine continues to be a versatile and valuable element in modern chemical applications.
Bromine (Br)
Where Found
Bromine is widely distributed in small quantities in the Earth’s crust. The oceans contain most of the world’s bromine, and it is also found in inland evaporitic(salt) lakes. Recovered from underground brines in Arkansas, bromine became that state’s most important mineral commodity and made the United States the producer of one-third of the world’s bromine. In descending order, Israel, China, Jordan, and Japan account for most of the balance.
Primary Uses
The use of bromine in flame retardants is a quickly expanding industry. Bromine is also used in agricultural applications, water treatment and sanitizing, petroleum additives, well-drilling fluids, dyes, photographic compounds, and pharmaceuticals.
Technical Definition
Bromine (abbreviated Br), atomic number 35, belongs to Group VII (the halogens) of the periodic table of the elements and resembles chlorine and iodine in its chemical properties. It has two naturally occurring isotopes: bromine 79 (50.69 percent) and bromine 81 (49.31 percent). Bromine is the only nonmetal that is liquid at room temperature. A volatile liquid, it is deep red in color with a density of 3.14 grams per cubic centimeter, a freezing point of -7.3° Celsius, and a boiling point of 58.8° Celsius. A diatomic element, bromine exists as paired bromine atoms in its elemental form.
Description, Distribution, and Forms
Bromine has an abundance of 2.5 parts per million in the Earth’s crust, ranking it forty-sixth in order of abundance of the elements. It is more prevalent in the oceans, at 65 parts per million. In salt lakes such as the Dead Sea, at 4,000 parts per million, and Searles Lake in California, at 85 parts per million, bromine is more abundant than in the oceans. The most concentrated sources of bromine are brinewells; one in Arkansas has 5,000 parts per million.
As a halogen, bromine needs one electron to achieve filled “s” (sharp) and “p” (principal) shells. Thus, bromine exists in nature as a bromide ion with a negative 1 charge. High concentrations of bromine in plants have not been noted. However, marine plants do have a relatively higher concentration than land plants.
Bromine, along with chlorine, tops the list of elements suspected of causing ozone depletion in the stratosphere. Because of this, the Environmental Protection Agency has listed methyl bromide and hydrobromofluorocarbons as a class I ozone-depleting substances. This classification means a limit to the production of these compounds in the United States.
Because availability has become more common because of pesticides and gasoline additives, the human intake of bromine has increased. There have not been toxicity problems, however, as bromine is retained for only short periods before it is excreted in urine. Plant and animals alike show little toxic reaction to bromine.
History
Antoine-Jérôme Balard first established bromine as an element. He had extracted bromine from brine by saturating it with chlorine and distilling. When attempts to decompose the new substance failed, he correctly deduced that bromine was an element and published his results in 1826. Balard wanted to call the new element “muride,” but the French Academy did not like the name. Bromine, from the Greek bromos, for stink or bad odor, was chosen instead. The first mineral of bromine found was bromyrite (silver bromide), found in Mexico in 1941. Silver bromide was used as the light-sensitive material in early photographic emulsions from about 1840, and potassium bromide began to be used in 1857 as a sedative and an anticonvulsant. The purple pigment known as Tyrian purple and referred to in Ezekiel in the Old Testament of the Bible is a bromine compound. Originally the dye was obtained from the small purple snail Murex brandaris.
Obtaining Bromine
Acidified solutions of bromine (either brines or seawater) are pumped into the top of a ceramic-filled tower. As the solution falls through the tower, the bromine reacts with chlorine. The chlorine becomes chloride ions dissolved in solution. The bromide ions in solution become bromine molecules. The bromine is then steamed out (collected in steam) or blown out (collected in air) by the steam or air passing through the tower. The bromine condenses and is separated from the gases at the top of the tower. It then can be purified or reacted with other substances to form bromine compounds. In Israel, the brine comes from the production of chemicals such as sodium chloride or potash and contains about 14,000 parts per million. Yearly world production of bromine in 2008 was about 400,000 metric tons (excluding U.S. production).
Uses of Bromine
Flame retardants use the highest percentage of the bromine produced, about 45. These products are used in circuit boards, television cabinets, wire, cable, textile coverings, wood treatments, fabric treatments, polyurethane foam insulation, and polyester resins. Bromine compounds are used in portable fire extinguishers as well as in closed spaces such as computer rooms. Use of bromine in agriculture as pesticides such as ethylene bromide, dibromochloropropane, or methyl bromide accounts for 10 percent of the total produced. Methyl bromide is a very effective nematocide (worm killer) as well as herbicide, fungicide, and insecticide. Bromine is also used in treating water and sanitizing water equipment such as swimming pools, hot tubs, water cooling towers, and food washing appliances. Bromine is more efficient than other materials because it has a higher biocidal activity.
In the 1970’s, the principal use of bromine was in ethylene dibromide, a scavenger for lead. With the decreased use of leaded gasoline, less ethylene dibromide is needed. High-density drilling fluids made with bromine compounds account for another 20 percent. Dyes and photography usage account for 5 percent. Silver bromide is still the main light-sensitive compound used in film. The pharmaceutical industry uses about 4 percent of the bromine produced. Because bromine is very reactive, forming compounds with every group except the noble gases, new uses for bromine will undoubtedly be found.
Bibliography
Greenwood, N. N., and A. Earnshaw. “The Halogens: Fluorine, Chloride, Bromine, Iodine, and Astatine.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Henderson, William. “The Group 17 (Halogen) Elements: Fluorine, Chlorine, Bromine, Iodine, and Astatine.” In Main Group Chemistry. Cambridge, England: Royal Society of Chemistry, 2000.
Jacobson, Mark Z. “Effects of Bromine on Global Ozone Reduction.” In Atmospheric Pollution: History, Science, and Regulation. New York: Cambridge University Press, 2002.
Kogel, Jessica Elzea, et al., eds. “Bromine.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006.
Krebs, Robert E. The History and Use of Our Earth’s Chemical Elements: A Reference Guide. Illustrations by Rae Déjur. 2d ed. Westport, Conn.: Greenwood Press, 2006.
Massey, A. G. “Group 17: The Halogens: Fluorine, Chlorine, Bromine, Iodine, and Astatine.” In Main Group Chemistry. 2d ed. New York: Wiley, 2000.
Weeks, Mary Elvira. Discovery of the Elements: Collected Reprints of a Series of Articles Published in the “Journal of Chemical Education.” Kila, Mont.: Kessinger, 2003.
U.S. Geological Survey.