Bromine (Br)

Stable isotopes of bromine available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Br-79 35 44 78.918338 50.69% >99.00% Sodium Bromide
Br-81 35 46 80.91629 49.31% >99.00% Sodium Bromide

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Bromine was discovered in 1825 and 1826 by Carl Jacob Löwig and Antoine-Jérôme Balard, respectively. It takes its name from the Greek word bromos, meaning “stench.” Its compounds were used well before it was recognized as an element: a purple dye called “Tyrian purple” was produced using an organobromine compound as well as an excretion from a particular kind of mussel.

Bromine is a dark reddish-brown liquid with a strong, disagreeable odor. It is the only nonmetallic element that remains a liquid at ambient temperatures; it solidifies at -7.2 ºC. It is sparingly soluble in water and soluble in common organic solvents. Most reactions of bromine are similar to those of other halogens, and its reactivity falls between those of chlorine and iodine. It readily attacks a number of metals, including alkali and alkaline earth metals, palladium, platinum, aluminum, copper, antimony and tin, forming their bromides, which are normally vigorous-to-violent reactions. It oxidizes a number of substances, including metal carbides, carbonyls, hydrides and organic substances. Bromine combines with fluorine at room temperature, forming bromine trifluoride. The reaction produces a luminous flame.

Combination reactions occur with several nonmetals. In aqueous solutions, bromine hydrolyzes slightly, forming unstable hypobromous acid, which decomposes to hydrobromic acid and oxygen, causing the bleaching action of bromine water. The decomposition is accelerated by light.

Bromine is used in bleaching fibers and as a disinfectant for water purification. Other applications are in organic synthesis as an oxidizing or brominating agent; in the manufacture of ethylene dibromide, methyl bromide and other bromo compounds for dyes and pharmaceutical uses; as a fire retardant for plastic; and in chemical analysis. Ethylene dibromide is used in anti-knock fluids in motor fuels. Over 80% of the bromine produced is consumed in the manufacture of this compound.

Most reactions of bromine are highly exothermic, which can cause incandescence or a sudden increase in pressure and rupture of reaction flasks. Reactions of liquid bromine with most metals (or any metal in finely divided state, metal hydrides, carbonyls and nitrides) can be explosive. Many oxides and halides of nonmetals, such as nitrogen triiodide or phosphorus trioxide, react explosively or burst into flame in contact with liquid bromine. Bromine is moderately toxic by all routes of exposure. It is an irritant to the eye and respiratory tract. Inhalation can cause dizziness, headache, coughing and lacrimation. A short exposure (to 1000 ppm for 15 minutes) can be fatal to humans. Ingestion produces nausea, abdominal pain and diarrhea. The liquid is corrosive to skin.

Properties of Bromine

Name Bromine 
Symbol Br 
Atomic number 35 
Atomic weight 79.904 
Standard state Liquid at 298 °K 
CAS Registry ID 7726-95-6 
Group in periodic table 17 
Group name Halogen 
Period in periodic table
Block in periodic table p-block 
Color Red-brown, metallic luster when solid 
Classification Non-metallic 
Melting point -7.3 °C
Boiling point 59 °C
Thermal conductivity 0.12  W/(m·K) 
Electrical resistivity 1 x 10-8 Ωm
Electronegativity 2.96 
Heat of vaporization 14.8 (per mole bromine atoms) kJ·mol-1 
Heat of fusion 5.8 (per mole bromine atoms) kJ·mol-1 
Density of liquid (Br2, liquid) 3.1028 g/cm-3 
Electron configuration [Ar]3d104s24p
Electron affinity  3.36359eV 
Most stable oxidation states  -1, +5 
Less stable oxidation states +1, +3
Critical temperature 315 ºC
Critical pressure 102 atm
Critical volume 127 cm3/mol