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Element Fact
Cesium is used in atomic clock. As in 1999, the best clock is accurate to a second in 20 million years.

Bromine, Br

bromine sample

Atomic number: 35
Atomic mass: 79.904(1)
Natural abundance: 2.5 ppm
79Br (78.918338) - 50.69%
81Br (80.916291) - 49.31%

History and Production

From Greek word bromos, meaning stench. The element was discovered by A.-J. Balard in 1826. In fact, J. von Liebig had missed identified a sample of bromine as iodine monochloride several years earlier. Bromine can be produced by oxidation of bromide ion with chlorine. The bromine source could be obtained from certain natural brine wells in Arkansas (4000-5000 ppm), the Dead Sea (4000-5000 ppm) and also in ocean waters (65 ppm). Bromine is mainly used to make ethylene dibromide which acts as a scavenger for lead from the anti-knock additive in gasoline. Such use is, however, become incresingly less important due to environmental considerations of lead in gasoline. Ethylene dibromide is also used as a general pesticide. Other uses of bromine, often as compounds, are dyestuffs, photography, pharmaceuticals, flameproofing agents etc.

Physical Data

Bromine is a heavy reddish-brown liquid. It is the only non-metal liquid element in the periodic table. It is volatile that gives a characteristic pungent smell. It is very reactive and when spilled it gives a painful sore. It is much less widely distribute than fluorine and chlorine which accounts only 2.5 ppm in the crustal rocks. Most of the bromine sources are from the ocean and also from salt lakes and brine wells.

Interatomic distance: 229 pm
Melting point: -7.2C
Boiling point: 58.8C
Thermal conductivity/Wm-1K-1: 0.122 (27C)
Density/kgm-3: 3122.6 (20C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 111.9 kJ/mol
Gibbs free energy of formation: 82.4 kJ/mol
Entropy: 175 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Ar] 3d10 4s2 4p5
Term symbol: 4P2
Electron affinity: 324.5371 kJ/mol   Electronegativity (Pauline): 2.96
Ionization energy (first, second, third): 1139.86, 2103.38, 3473.47 kJ/mol

Chemical properties

Test for bromine (bromide ion):
(1) Addition of silver nitrate to a solution of a bromide in nitric aid produces a pale yellow-white (cream) colored precipitate of silver bromide, soluble in ammonia.
(2) Addition of concentrated sulfuric acid to a solid bromide produces hydrobromic acid and some brown vapor of bromine.
(3) Addition of chlorine water to a bromide solution liberates bromine via displacement reaction, which gives the solution brown.


A. Rocke, 'Bromine, brines and bleaches', Chemistry in Britain, Vol. 38, March 2002.

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