bromine


bromine
/broh"meen, -min/, n. Chem.
an element that is a dark-reddish, fuming, toxic liquid and a member of the halogen family: obtained from natural brines and ocean water, and used chiefly in the manufacture of gasoline antiknock compounds, pharmaceuticals, and dyes. Symbol: Br; at. wt.: 79.909; at. no.: 35; sp. gr.: 3.119 at 20°C.
[1827; < F brome bromine ( < Gk brômos stench) + -INE2]

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Nonmetallic chemical element, chemical symbol Br, atomic number 35.

One of the halogens, it is a deep red, fuming liquid at ordinary temperatures (freezing point 19 °F [-7.2 °C]; boiling point 138 °F [59 °C]) that contains diatomic molecules (Br2), and it does not occur free in nature. It is obtained from seawater and brines or salt beds. Extremely irritating and toxic, bromine is a strong oxidizing agent (see oxidation-reduction). Its compounds, in which it may have valence 1, 3, 5, or 7, have many uses, including as petroleum additives (ethylene dibromide), in photographic emulsions (silver bromide), as sedatives, and in flour (potassium bromate).

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Introduction
 chemical element, a deep red, noxious liquid, and a member of the halogen elements (halogen element), or Group 17 (Group VIIa) of the periodic table (periodic law).

History
      Bromine was discovered in 1826 by the French chemist Antoine-Jérôme Balard (Balard, Antoine-Jérôme) in the residues (bitterns) 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. (The German chemist Justus von Liebig (Liebig, Justus, Freiherr von) appears to have obtained the element before Balard, but he wrongly considered it to be iodine chloride.) 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.”

Occurrence and distribution
      A rare element, bromine is found in nature dispersed throughout Earth's (Earth) 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 (isotope): 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).

Physical and chemical properties
      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 (halogen element), bromine exists as diatomic molecules (molecule) in all aggregation states.

      About 3.41 grams (0.12 ounce) of bromine dissolve in 100 millilitres (0.1 quart) of water at room temperature. The solution is known as bromine water. Like chlorine water, it is a good oxidizing agent, and it is more useful because it does not decompose so readily. It liberates free iodine from iodide-containing solutions and sulfur from hydrogen sulfide. Sulfurous acid is oxidized by bromine water to sulfuric acid. In sunlight bromine water decomposes, with release of oxygen, as in the following equation:

      From bromine water a hydrate (a clathrate) can be isolated that contains 172 water molecules and 20 cavities capable of accommodating the bromine molecules. Bromine dissolves in aqueous alkali hydroxide solutions, giving bromides, hypobromites, or bromates, depending on the temperature. Bromine is readily extracted from water by organic solvents such as carbon tetrachloride, chloroform, or carbon disulfide, in which it is very soluble. In the organic solvents it gives an orange solution.

      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. Similarly, a metal-bromine bond is weaker than the corresponding metal-chlorine bond, and this difference is reflected in the chemical reactivity of bromine, which lies between that of chlorine and that of iodine. An organic bromo compound resembles the corresponding chloro derivative but is usually more dense, less volatile, less combustible, and less stable.

      Bromine combines violently with the alkali metals (alkali metal) and with phosphorus, arsenic, aluminum, and antimony but less violently with certain other metals. Bromine displaces hydrogen from saturated hydrocarbons (hydrocarbon) and adds to unsaturated hydrocarbons, though not as readily as chlorine does.

      The most stable oxidation state of the element is −1, in which bromine occurs naturally. But oxidation states of 0 (elemental bromine, Br2), +1 (hypobromite, BrO), +3 (bromite, BrO2), +5 (bromate, BrO3), and +7 (perbromate, BrO4) are also known. The first ionization energy of bromine is high, and compounds containing bromine in positive oxidation numbers are stabilized by appropriate ligands (ligand), mainly oxygen and fluorine. Compounds with the oxidation numbers +1, +3, +4, +5, and +7 all contain covalent bonds (covalent bond).

Production and use
      The chief commercial source of bromine is ocean water, from which the element is extracted by means of chemical displacement (oxidation) by chlorine in the presence of sulfuric acid through the reaction

      The product of the reaction is a dilute solution of bromine, from which the element is removed by blowing air through it. The free bromine is then mixed with sulfur dioxide, and the mixed gases are passed up a tower down which water is trickling. The following reaction takes place in the tower:

      resulting in a mixture of acids that is much richer in bromide ion than seawater. A second treatment with chlorine liberates bromine, which is freed from chlorine and purified by passage over moist iron filings.

      Commercial bromine generally contains up to 0.3 percent chlorine. It is usually stored in glass bottles or in barrels coated with lead or Monel metal.

      The industrial usage of bromine had been dominated by the compound ethylene bromide (C2H4Br2), which once was added to gasoline with tetraethyl lead to prevent deposition of lead in the engine. Since the renunciation of leaded gasoline, bromine compounds have mainly been used in flame retardants, but ethylene bromide is still an important compound because of its use to destroy nematodes (nematode) and other pests in soils. Bromine is also used in the production of catalysts (catalyst), such as aluminum bromide.

      Bromine has other uses, as in making various dyes (dye) and the compounds tetrabromoethane (C2H2Br4) and bromoform (CHBr3), which are used as liquids in gauges because of their high specific gravity. Until the development of barbiturates (barbiturate) in the early 20th century, bromides of potassium, sodium, calcium, strontium, lithium, and ammonium were used widely in medicine because of their sedative action. Silver bromide (AgBr), an important component of photographic film, is, like silver chloride and iodide, light sensitive. Traces of potassium bromate (KBrO3) are added to wheat flour to improve baking. Other bromine compounds of significance include hydrogen bromide (HBr), a colourless gas used as a reducing agent and a catalyst in organic reactions. A solution of the gas in water is called hydrobromic acid, a strong acid that resembles hydrochloric acid in its activity toward metals (metal) and their oxides (oxide) and hydroxides (hydroxide).

Analysis
      A sensitive test for bromine is the reaction with fluorescein to give a deep red colour caused by bromination of the organic molecule, or by its reaction with fuchsine dyes in the presence of sulfurous acid, to give a deep blue colour. A more common test involves heating the sample with dilute sulfuric acid in the presence of potassium dichromate; the bromine is then extracted with chloroform, and, upon addition of potassium iodide, the pink colour of iodine appears. The presence of bromine may also be recognized by the evolution of hydrogen bromide containing some brown bromine vapour when a solid sample is treated with concentrated sulfuric acid. Alternatively, chlorine may be added to an aqueous solution of a sample containing bromide, causing development of a brown colour (free bromine).

      For the quantitative determination of bromine, the following methods are recommended:
      Free bromine is titrated with sodium thiosulfate in the presence of potassium iodide:

      Bromides may be determined either gravimetrically (by weight analysis) or by titration with silver nitrate:

      In the presence of chloride and iodide, the potentiometric method may be used (as with chlorine).

      In the absence of iodide, bromide may be oxidized to bromine, which is then determined in the distillate. Alternatively, bromide may be oxidized to bromate by hypochlorous acid. The excess of the oxidizing agent is destroyed by sodium formate, and iodine is liberated by addition of potassium iodide and acid, with the free iodine being titrated by thiosulfate.

      For the determination of bromine in an organic compound, the latter is oxidized by nitric acid, and the bromine is determined as silver bromide.

atomic number
35
atomic weight
79.909
melting point
−7.2 °C (19 °F)
boiling point
59 °C (138 °F)
specific gravity
3.12 (20 °C, or 68 °F)
oxidation states
−1, +1, +3, +5, +7
electronic config.
(Ar)3d104s24p5
Karl Christe Stefan Schneider

Additional Reading
The chemistry of bromine is treated in D. Price, B. Iddon, and B.J. Wakefield (eds.), Bromine Compounds: Chemistry and Applications (1988).

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Universalium. 2010.

Look at other dictionaries:

  • Bromine — (pronEng|ˈbroʊmiːn/, /ˈbroʊmaɪn/, /ˈbroʊmɪn, el. βρῶμος, brómos , meaning stench (of he goats) Gemoll W, Vretska K: Griechisch Deutsches Schul und Handwörterbuch ( Greek German dictionary ), 9th ed., published by [http://www.oebvhpt.at/ öbvhpt] …   Wikipedia

  • Bromine — Bro mine, n. [Gr. ? bad smell, stink. Cf. {Brome}.] (Chem.) One of the halogen elements, related in its chemical qualities to chlorine and iodine. Atomic weight 79.8. Symbol Br. It is a deep reddish brown liquid of a very disagreeable odor,… …   The Collaborative International Dictionary of English

  • bromine — Symbol: Br Atomic number: 35 Atomic weight: 79.909 Halogen element. Red volatile liquid at room temperature. Its reactivity is somewhere between chlorine and iodine. Harmful to human tissue in a liquid state, the vapour irritates eyes and throat …   Elements of periodic system

  • bromine — nonmetallic element, 1827, from Fr. brome, from Gk. bromos stench. With chemical suffix INE (Cf. ine) (2). The evil smelling dark red liquid was discovered by French chemist Antoine Jérôme Balard (1802 1876), who initially called it muride …   Etymology dictionary

  • bromine — ► NOUN ▪ a dark red liquid chemical element of the halogen group, with a choking irritating smell. ORIGIN from Greek br mos a stink …   English terms dictionary

  • bromine — [brō′mēn΄, brō′min] n. [Fr brome < Gr brōmos, stench + INE3] a chemical element, one of the halogens, usually in the form of a reddish brown, corrosive liquid, that volatilizes to form a vapor that has an unpleasant odor and is very irritating …   English World dictionary

  • bromine —   n. non metallic chlorine like element found in seawater and mineral springs.    ♦ bromize, v.t. compound with bromine; prepare photographic plate with bromide.    ♦ bromism, n. condition due to excessive use of bromide.    ♦ brominated,   a.… …   Dictionary of difficult words

  • bromine — noun Etymology: French brome bromine + English 2 ine Date: 1827 a nonmetallic halogen element that is isolated as a deep red corrosive toxic volatile liquid of disagreeable odor see element table …   New Collegiate Dictionary

  • bromine — noun /ˈbrəʊmɪn,ˈbrəʊmaɪn,ˈbroʊmin/ a) A nonmetallic chemical element (symbol Br) with an atomic number of 35; one of the halogens b) A bromine atom in a molecule Syn: muride See Also: brome …   Wiktionary

  • bromine — bro•mine [[t]ˈbroʊ min, mɪn[/t]] n. chem. a dark reddish, fuming, toxic liquid element obtained from natural brines and ocean water and used chiefly in gasoline antiknock compounds, pharmaceuticals, and dyes Symbol: Br at. wt.: 79.909 at. no.: 35 …   From formal English to slang


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