Bromine (revised)
BROMINE (REVISED)
Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Overview
Bromine is a member of the halogen family. Halogens are the elements that make up Group 17 (VIIA) of the periodic table. The periodic table is a chart that shows how elements are related to one another. The halogens are also known as the salt formers. Fluorine, chlorine, bromine, iodine, and astatine form salts when chemically combined with a metal.
Bromine was discovered, at almost the same time in 1826, by two men, German chemist Carl Lowig (1803-90) and French chemist Antoine-Jerome Balard (1802-76). While Balard announced his discovery first, Lowig had simply not completed his studies of the element when Balard made his announcement.
SYMBOL
Br
ATOMIC NUMBER
35
ATOMIC MASS
79.904
FAMILY
Group 17 (VIIA)
Halogen
PRONUNCIATION
BRO-meen
Nearly 90 percent of all bromine produced comes from the United States, Israel, or the United Kingdom. In 1996, about 450,000,000 kilograms (one billion pounds) of the element were produced worldwide. The largest single use of the element is in the manufacture of flame retardants. Flame retardants are chemicals added to materials to prevent burning or to keep them from burning out of control. Other major uses are in the manufacture of drilling fluids, pesticides, chemicals for the purification of water, photographic chemicals, and as an additive to rubber.
Discovery and naming
Compounds of bromine had been known for hundreds of years before the element was discovered. One of the most famous of these compounds was Tyrian purple, also called royal purple. (Tyrian comes from the word Tyre, an ancient Phoenician city.) Only very rich people or royalty could afford to buy fabric dyed with Tyrian purple. It was obtained from a mollusk (shell fish) found on the shores of the Mediterranean Sea (a large body of water bordered by Europe, Asia, and Africa).
In 1825, Löwig enrolled at the University of Heidelberg in Germany to study chemistry. He continued an experiment he had begun at home in which he added chlorine to spring water. The addition of ether to that mixture produced a beautiful red color. Löwig suspected he had discovered a new kind substance. A professor encouraged him by suggesting he study the substance in more detail.
As these studies progressed, Balard published a report in a chemical journal that announced the discovery of the new element bromine. The element had all the properties of Löwig's new substance. The two chemists had made the discovery at nearly the same time! Balard, however, is credited as the discoverer of bromine, because scientists acknowledge the first person to publish his or her findings.
In Greek, the word bromos means "stench" (strong, offensive odor). Bromine lives up to the description. The odor is intense and highly irritating to the eyes and lungs.
Chemists found that bromine belonged in the halogen family. They knew that it had properties similar to other halogens and placed it below fluorine and chlorine in the periodic table.
Physical properties
Only two liquid elements exist—bromine and mercury. At room temperature, bromine is a deep reddish-brown liquid. It evaporates easily, giving off strong fumes that irritate the throat and lungs. Bromine boils at 58.8°C (137.8°F), and its density is 3.1023 grams per cubic centimeter. Bromine freezes at -7.3°C (18.9°F).
Bromine dissolves well in organic liquids—such as ether, alcohol, and carbon tetrachloride—but only slightly in water. Organic compounds contain the element carbon.
Chemical properties
Bromine is a very reactive element. While it is less reactive than fluorine or chlorine, it is more reactive than iodine. It reacts with many metals, sometimes very vigorously. For instance, with potassium, it reacts explosively. Bromine even combines with relatively unreactive metals, such as platinum and palladium.
Occurrence in nature
Bromine is too reactive to exist as a free element in nature. Instead, it occurs in compounds, the most common of which are sodium bromide (NaBr) and potassium bromide (KBr). These compounds are found in seawater and underground salt beds. These salt beds were formed in regions where oceans once covered the land. When the oceans evaporated (dried up), salts were left behind—primarily sodium chloride (NaCl),potassium chloride (KCl), and sodium and potassium bromide. Later, movements of the Earth's crust buried the salt deposits. Now they are buried miles underground. The salts are brought to the surface in much the same way that coal is mined.
Bromine is a moderately abundant element. Its abundance in the Earth's crust is estimated to be about 1.6 to 2.4 parts per million. It is far more abundant in seawater where it is estimated at about 65 parts per million.
In some regions, the abundance of bromine is even higher. For example, the Dead Sea (which borders Israel and Jordan), has a high level of dissolved salts. The abundance of bromine there is estimated to be 4,000 parts per million. The salinity, or salt content, is so high that nothing lives in the water. This is why it is called the Dead Sea.
Isotopes
Two naturally existing isotopes of bromine exist, bromine-79 and bromine-81. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
At least 16 radioactive isotopes of bromine are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
No isotope of bromine has any important commercial use.
The salinity, or salt content, is so high that nothing lives in the water. This is why it is called the Dead Sea.
Extraction
The method used by Lowig and Balard to collect bromine continues to be used today. Chlorine is added to seawater containing sodium bromide or potassium bromide. Chlorine is more active than bromine and replaces bromine in the reaction:
Uses
The most important use of bromine today is in making flame retardant materials. Many materials used in making clothing, carpets, curtains, and drapes are flammable, and if a flame touches them, they burn very quickly. Chemists have learned how to make materials more resistant to fires by soaking them in a bromine compound. The compound coats the fibers of the material. The bromine compound can also be chemically incorporated into the material.
The bromine compounds used in flame retardants are often complicated. One such compound is called tris(dibromopropyl)phosphate ((Br2C3H5O)3PO). However, this compound has been found to be a carcinogen (cancer-causing substance). Its use, therefore, has been severely restricted.
About 20 percent of all bromine is used in drilling wells. Calcium bromide (CaBr2), sodium bromide (NaBr), or zinc bromide (ZnBr2) are added to the well to increase the efficiency of the drilling process.
Bromine is also important in the manufacture of pesticides, chemicals used to kill pests. Methyl bromide (CH3Br) has been used for years to treat crop lands. Methyl bromide is sprayed on the surface or injected directly into the ground.
Some methyl bromide always evaporates into the air where it damages the ozone layer. Ozone (O3) gas filters out a portion of the ultraviolet (UV) radiation from the sun. UV radiation causes skin cancer, sunburn, and damage to plants and fragile organisms.
Worldwide production of methyl bromide will end in 2001 because of its effect on the ozone layer. The United States plans to stop production of the compound even earlier. Farmers believe nothing works as well as methyl bromide in eliminating certain pests. They are concerned that crop production will suffer if methyl bromide is banned.
The most important use of bromine today is in making flame retardant materials.
Ethylene dibromide (C2H4Br2) is a bromide compound added to leaded gasoline. The lead in "leaded gasoline" is tetraethyl lead (Pb(C2H5))4). It helps fuels burn more cleanly and keeps car engines from "knocking." "Knocking" is a repetitive metallic banging sound that occurs when there are ignition problems with a car's engine. "Knocking" reduces the efficiency of a car engine.
But leaded gasoline gives off free lead as it burns. Free lead is a very toxic element that causes damage to the nervous system. Ethylene dibromide is added to react with free lead and convert it to a safe compound.
Ethylene dibromide does not completely solve the problem. Some free lead still escapes into the atmosphere. Leaded gasoline has been banned in the United States for many years but is still used in other countries.
The most popular element for purifying public water supplies and swimming pools used to be chlorine. Bromine compounds have become more popular for their superior bacteria killing power.
Health effects
Bromine is toxic if inhaled or swallowed. It can damage the respiratory system and the digestive system, and can even cause death. It can also cause damage if spilled on the skin.
Bromine
Bromine
Bromine is an element that belongs to Group 17 on the periodic table of elements, the group that contains substances called halogens. Other halogens include fluorine, chlorine , and iodine. Halogens are important elements that are used in heavily in industry. Bromine is used in the manufacture of dyes, fumigants, fire-retardant materials, medicines, pesticides, and photographic emulsions. Bromine is also used for water purification. While bromine and bromine-containing products are very useful, some concern surrounds the use of some bromine compounds because of their impact on the environment , particularly the ozone layer.
The many uses of bromine are due to its chemical properties. The halogens are the most reactive non-metal elements in the periodic table. Halogens characteristically react very rapidly and readily with almost all metals to form salts. The high reactivity of the halogens is due to the presence of seven (rather than the stable noble-gas configuration of eight) electrons in their outer shell. Thus, they have an unpaired electron that is readily available for chemical bonding and reactions with other elements. Unlike chlorine and iodine, bromine is a liquid at room temperature. It is the only liquid nonmetallic element.
Bromine is a fairly heavy inorganic element. First isolated in 1826, the atomic number of bromine is 35, which means it has 35 electrons and 35 protons. Bromine also contains 45 neutrons in its nucleus, making its average atomic mass 79.9 atomic mass units. At room temperature, it is a reddish-brown liquid that emits pungent, noxious fumes that irritate the eyes. Appropriately, the word bromine is derived from the Greek word bromos, which means "stench." Bromine readily dissolves in water and carbon disulfide. It has a boiling point of 138.6°F(59.2°C) and is more reactive than iodine, but less reactive than chlorine. When bromine chemically reacts with other elements or compounds, it has a bleaching effect. It is a fairly strong oxidizing agent . Relative to the other halogens, bromine is a stronger oxidizing agent than iodine, but a weaker oxidizer than both chlorine and fluorine. Even so, liquid bromine is very caustic and can seriously damage skin on contact. Bromine, like the other halogens, has a very high affinity for itself, and therefore forms diatomic molecules, which are molecules that contain only two atoms. Molecular bromine exists as two bromine atoms bonded together.
Bromine is obtained from natural salt deposits. Two areas within the United States that have historically been associated with bromine extraction are Arkansas and Michigan. Bromine may also be extracted from seawater. Aqueous bromine may also be produced from the oxidation of bromides during chlorination of water, especially when seawater is used as a coolant. Since it contains a very slight concentration of bromine salts (about 85 parts per million ), seawater is not a major source of industrial bromine. The most common form of mineralized bromine is silver bromide (bromargyrite), found chiefly in Mexico and Chile. Most of the supply of bromine used for industrial purposes, however, comes from the United States and Israel, with smaller amounts produced in France, Japan, and Russia.
Bromine-containing substances have been used for centuries. The first use of a material containing bromine was in ancient Rome. During the Roman Empire, a highly prized purple dye was painstakingly extracted from marine mussels. The dye, a bromine compound, was very expensive because it was so difficult to obtain and only the very wealthy could afford clothing dyed with the hue of this dye, which resulted in the term "royal purple." Nowadays, bromine is used not only the production of dyes, but also in the production of chemicals that improve safety, agriculture, and sanitation .
Bromine is a very effective agent in controlling the growth of aquatic microorganisms . As such, and like chlorine, it is used for water treatment because it can kill microorganisms and keep water clear and free from foul odors. For example, bromine salts, like sodium bromide, are used to control the growth of algae and bacteria in recreational spaces like hot tubs and swimming pools. Another common bromine aquatic biocide is bromochlorodimethylhydantoin. Occasionally, bromine is used by municipalities to control disease-causing microbes in drinking water because some of these microorganisms are more susceptible to bromine than chlorine.
Bromine compounds are also used as pesticides. Like other halogenated hydrocarbons such as DDT, some brominated hydrocarbons are powerful insecticides. A very effective and important bromine-containing hydrocarbon pesticide is methyl bromide. This agent, also known as bromomethane, is used to fumigate stored grain and produce to free them from pest infestations. Methyl bromide is also used to fumigate soil for valuable crops like strawberries, peppers, eggplants, tomatoes, and tobacco . Since the 1940s, methyl bromide has been used as a soil pretreatment to kill insect, roundworm, and weed species that decrease the productivity of economically important crops. In 1992, approximately 73,000 tons of methyl bromide were used. However it was discovered that methyl bromide, like chlorofluorocarbons , also contributes to the depletion of the ozone layer. As a result, the Environmental Protection Agency (EPA) made recommendations that its use be phased-out based upon the expert assessments of atmospheric scientists from the World Meteorological Organization and the National Oceanic and Atmospheric Administration . Under the Clean Air Act , the EPA is enforcing reductions in the use of methyl bromide. A mandatory reduction of 25% was achieved in 1999. By 2001, 50% reduction had been enforced. By the year 2003, a 70% reduction in the use of methyl bromide must be attained with a goal for a complete ban of the compound scheduled for the year 2005.
Despite the ban on methyl bromide, bromine will continue to be a valued chemical. The pharmaceutical industry relies heavily on bromine both in the manufacturing process and as constituent substance in pharmaceutical agents. The general anesthetic, halothane, contains bromine. The production of naproxen sodium, an over-the-counter non-steroidal analgesic, uses bromine in intermediate reactions. Brompheniramine, the widely available antihistamine cold and allergy medication, contains bromine. The synthetic addition of bromine, or other halogens, to medications such as these facilitates their uptake into tissues. Other drugs use bromine to create easily absorbed dosage forms. For example, dextromethorphan hydrobromide, a cough medication, is a soluble bromine salt form of the poorly soluble active drug dextromethorphan, and dissolves easily as a clear solution.
Bromine is also used to create fire-resistant plastics . Plastic is made of very flammable hydrocarbon polymers. The addition of bromine compounds creates fire-retardant plastic products. Brominated flame-retardants are used in televisions, stereos, computers, and electrical wiring to reduce fire hazard when these common electronic appliances generate excessive heat. Brommine-containing fire-retardant chemicals are also used in carpeting, draperies, and furniture foam padding. While bromine compounds make products more fire-resistant, they do not make them fire-proof. Rather, they reduce the likelihood that a plastic item will ignite and delay the spread of fire. As bromine-treated plastic products burn, they release brominated hydrocarbons that threaten the ozone layer not unlike chorofluorocarbons (CFCs). For this reason, research is now directed at finding alternatives to bromine flame-retardant chemicals. For example, promising new fire-resistant compounds use silicon.
Aside from its use in dyes, pesticides, water treatment, pharmaceuticals, and fire retardants, bromine compounds are also used in photographic film and print paper emulsions, hydraulic fluids, refrigeration fluids, inks, and hair products. As useful as bromine is, however, concern for the ozone layer has resulted in heightened vigilance concerning the overuse of bromine-containing chemicals.
[Terry Watkins ]
RESOURCES
BOOKS
Nilsson, Annika. Ultraviolet Reflections: Life Under a Thinning Ozone Layer. New York: John Wiley & Son Ltd, 1996.
Price, D. et al. Bromine Compounds: Chemistry and Applications. New York: Elsevier Science Ltd., 1988.
PERIODICALS
Alaee, M. and Wenning, R. J. "The significance of brominated flame retardants in the environment: current understanding, issues and challenges." Chemosphere. 46, no. 5 (February, 2000): 579-582.
Anbar, A.D. et al. "Methyl bromide: ocean sources, ocean sinks, and climate sensitivity." Global Biogeochemistry Cycles 10, no. 1 (March, 1996): 175-190.
Rhew, R. C. et al. "Natural methyl bromide and methyl chloride emissions from coastal salt marshes." Nature 403, no. 6767 (January, 2000): 292-295.
OTHER
Winter, Mark. Bromine. WebElements Periodic Table. <http://www.webelements.com/webelements/scholar/index.html>
Bromine
Bromine
melting point: −7.3°C
boiling point: 59°C
density: 3.12 g/cm3 (liq. at 20°C)
most common ions: Br−, BrO−, BrO3−, BrO4−
Bromine is a member of a family of elements known as halogens that are found in group 7A of the Periodic Table. Bromine was discovered in 1826 in Montpellier, France, by French chemist Antoine J. Balard.
Bromine is one of two elements (the other being mercury) that is liquid at normal temperatures. As with the other halogens, bromine is very reactive, corrosive, and poisonous. Both the liquid and vapor of bromine are deep red in color. Bromine has a pungent, irritating odor that is the source of the element's name (the Greek word bromos means "stench").
Elemental bromine is a diatomic molecule (Br2). Bromine will combine with most other elements. Reaction with metallic elements leads to salts such as silver bromide (AgBr), in which the bromine atom has a −1 charge and oxidation number. Bromine forms many interesting covalent compounds as well, including two oxides: bromine (IV) oxide (BrO2) and bromine (I) oxide (Br2O).
Bromine is produced commercially from natural brines and from sea-water either by electrolysis or with displacement by chlorine, a somewhat more reactive halogen. The concentration of bromine in seawater is approximately 67 parts per million (ppm) by weight; it is found in Earth's crust at an average level of 3 ppm.
Bromine compounds have a variety of uses. Methyl bromide (CH3Br) is a common agricultural soil fumigant; other bromohalocarbon compounds have been used as refrigerants and fire suppressants. Inorganic bromides are important components of photographic emulsions. Bromine reacts with liquid water to produce hypobromite ion (BrO−), a powerful bleaching agent. There are also many dyes and pharmaceutical agents that contain bromine.
see also Halogens.
John Michael Nicovich
Bibliography
Lide, David R., ed. (2003). The CRC Handbook of Chemistry and Physics, 84th edition. Boca Raton, FL: CRC Press.
Internet Resources
Winter, Mark. "Bromine." The University of Sheffield and WebElements Ltd., U.K. Available from <http://www.webelements.com>.
bromine
bromine
bro·mine / ˈbrōmēn/ • n. the chemical element of atomic number 35, a dark red fuming toxic liquid with a choking, irritating smell. It is a member of the halogen group and occurs chiefly as salts in seawater and brines. (Symbol: Br)