Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest halogen and is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between those of chlorine and iodine. Isolated independently by two chemists, Carl Jacob Löwig (in 1825) and Antoine Jérôme Balard (in 1826), its name was derived from the Ancient Greek βρῶμος (meaning "stench"), referring to its sharp and pungent smell.

Bromine, 35Br
Liquid and gas bromine inside transparent cube
Pronunciation/ˈbrmn, -mɪn, -mn/ (BROH-meen, -min, -myne)
Standard atomic weight Ar°(Br)
  • [79.901, 79.907]
  • 79.904±0.003 (abridged)[1]
Bromine in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)35
Groupgroup 17 (halogens)
Periodperiod 4
Block  p-block
Electron configuration[Ar] 3d10 4s2 4p5
Electrons per shell2, 8, 18, 7
Physical properties
Phase at STPliquid
Melting point(Br2) 265.8 K (−7.2 °C, 19 °F)
Boiling point(Br2) 332.0 K (58.8 °C, 137.8 °F)
Density (near r.t.)Br2, liquid: 3.1028 g/cm3
Triple point265.90 K, 5.8 kPa[2]
Critical point588 K, 10.34 MPa[2]
Heat of fusion(Br2) 10.571 kJ/mol
Heat of vaporisation(Br2) 29.96 kJ/mol
Molar heat capacity(Br2) 75.69 J/(mol·K)
Vapour pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 185 201 220 244 276 332
Atomic properties
Oxidation states−1, +1, +3, +4, +5, +7 (a strongly acidic oxide)
ElectronegativityPauling scale: 2.96
Ionisation energies
  • 1st: 1139.9 kJ/mol
  • 2nd: 2103 kJ/mol
  • 3rd: 3470 kJ/mol
Atomic radiusempirical: 120 pm
Covalent radius120±3 pm
Van der Waals radius185 pm
Spectral lines of bromine
Other properties
Natural occurrenceprimordial
Crystal structure orthorhombic
Speed of sound206 m/s (at 20 °C)
Thermal conductivity0.122 W/(m⋅K)
Electrical resistivity7.8×1010 Ω⋅m (at 20 °C)
Magnetic orderingdiamagnetic[3]
Molar magnetic susceptibility−56.4×10−6 cm3/mol[4]
CAS Number7726-95-6
Discovery and first isolationAntoine Jérôme Balard and Carl Jacob Löwig (1825)
Main isotopes of bromine
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
79Br 51% stable
81Br 49% stable
 Category: Bromine
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Elemental bromine is very reactive and thus does not occur free in nature, but in colourless soluble crystalline mineral halide salts, analogous to table salt. While it is rather rare in the Earth's crust, the high solubility of the bromide ion (Br) has caused its accumulation in the oceans. Commercially the element is easily extracted from brine evaporation ponds, mostly in the United States, Israel, and China. The mass of bromine in the oceans is about one three-hundredth that of chlorine.

At standard conditions for temperature and pressure it is a liquid; the only other element that is liquid under these conditions is mercury. At high temperatures, organobromine compounds readily dissociate to yield free bromine atoms, a process that stops free radical chemical chain reactions. This effect makes organobromine compounds useful as fire retardants, and more than half the bromine produced worldwide each year is put to this purpose. The same property causes ultraviolet sunlight to dissociate volatile organobromine compounds in the atmosphere to yield free bromine atoms, causing ozone depletion. As a result, many organobromine compounds—such as the pesticide methyl bromide—are no longer used. Bromine compounds are still used in well drilling fluids, in photographic film, and as an intermediate in the manufacture of organic chemicals.

Large amounts of bromide salts are toxic from the action of soluble bromide ions, causing bromism. However, a clear biological role for bromide ions and hypobromous acid has recently been elucidated, and it now appears that bromine is an essential trace element in humans. The role of biological organobromine compounds in sea life such as algae has been known for much longer. As a pharmaceutical, the simple bromide ion (Br) has inhibitory effects on the central nervous system, and bromide salts were once a major medical sedative, before replacement by shorter-acting drugs. They retain niche uses as antiepileptics.

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