Bromine is a chemical element with the symbol Br and atomic number 35. It 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 (bromos) meaning "stench", referring to its sharp and pungent smell.

Elemental bromine is very reactive and thus does not occur as a free element in nature. Instead, it can be isolated from colourless soluble crystalline mineral halide salts analogous to table salt, a property it shares with the other halogens. 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 and Israel. 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, bromine is beneficial for human eosinophils, and is an essential trace element for collagen development in all animals. Hundreds of known organobromine compounds are generated by terrestrial and marine plants and animals, and some serve important biological roles. 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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Atomic properties

Standard atomic weight79.904 ±0.003 [79.901 … 79.907]
Atomic mass79.9047 u

Atomic radii

Radius (empirical)120 pm
Radius (calculated)94 pm
Covalent radius120 ±3 pm
Van der Waals radius185 pm

Atomic shell

Electron configurationAr 3d10 4s2 4p5
Ionization energy(1st) 11.81381 eV
(2nd) 21.591 eV
(3rd) 34.871 eV
(4th) 47.782 eV
(5th) 59.595 eV
(6th) 87.39 eV
(7th) 103.03 eV
Shell model

Physical properties

Density3.12 g·cm−3 (300 K)
Molar volumesolid: 1.978·10-5 m3·mol−1


Melting point265.8 K
Boiling point332 K
Liquid range66.2 K
Triple point265.9 K @ 5.8 kPa
Critical point588 K @ 10.34 MPa
Transition temperature1.4 K


Melting enthalpy5.8 kJ·mol-1
Enthalpy of vaporization14.8 kJ·mol-1
Binding energy112 kJ·mol-1

Heat and conductivity

Thermal conductivity0.12 W·m-1·K-1

Elastic properties

Bulk modulus1.9 GPa

Electrical properties

Resistance1·1011 Ωm


Magnetic susceptibility-5.641·10-5 cm3·mol−1

Optical properties

Refractive index1.001

Chemical properties

Basicitystrongly acidic
Oxidation state±1, 3, 5, 7
Standard potential1.066 V (Br + e- → Br-)


Pauling scale2.96
Sanderson scale3.22
Allred-Rochow scale2.74
Mulliken scale2.95
Allen scale2.685
Ghosh-Gupta scale6.165 eV
Boyd-Edgecombe scale2.75
Nagle scale2.56
Pearson absolute negativity7.59 eV

Other properties

Natural occurrenceprimordial
Crystal structureOrthorhombic
Goldschmidt Classificationlithophile
Superconductorwith transition tempperature under special conditions
Price/kg4.39 USD

Natural abundances

7 ppb ≈ 7.03·1010 M☉
1,200 ppb ≈ 1.2 g
Earth’s crust
3,000 ppb ≈ 83,100 Mt
67,300 ppb ≈ 92.2 Mt
Flowing water
20 ppb ≈ 320 kt
Human body
2,900 ppb ≈ 203 mg