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Bromine

physical science Maturity 11-13 Next article →

Bromine is a chemical element identified by the symbol Br and atomic number 35. It is a volatile, reddish-brown liquid at room temperature.

Bromine vial in acrylic cube
Bromine vial in acrylic cube

Because it evaporates so easily, it quickly forms a similarly colored vapor. This element belongs to the halogen group on the periodic table.

Orthorhombic
Orthorhombic

In this group, bromine sits between chlorine and iodine. Its chemical properties are intermediate between these two neighboring halogens. This means it is more reactive than iodine but less reactive than chlorine.

The chemistry of bromine is driven by its electron configuration. It has seven electrons in its outermost shell.

Alkene-bromine-addition-2D-skeletal
Alkene-bromine-addition-2D-skeletal

Because it is one electron short of a full octet, it acts as a strong oxidizing agent. This means it reacts readily with other elements to complete its shell. Its electronegativity, which measures how strongly an atom pulls on electrons, is 2.96. This value is between chlorine at 3.16 and iodine at 2.66. In its solid form, bromine crystallizes in an orthorhombic system.

Orthorhombic
Orthorhombic

This structure consists of layered arrangements of Br2 molecules. Because of this molecular structure, liquid bromine is a very poor conductor of electricity. However, at extreme pressures of 55 GPa, it undergoes a transition from an insulator to a metal.

Bromine is very reactive, so it never occurs as a free element in nature. Instead, it is found within soluble crystalline mineral halide salts. These salts are similar to common table salt. While bromine is somewhat rare in the Earth's crust, it accumulates in the oceans. This happens because the bromide ion, or Br−, is highly soluble in water.

STS028-96-65
STS028-96-65

The total mass of bromine in the oceans is about one three-hundredth the mass of chlorine. Today, bromine is extracted commercially from brine evaporation ponds. Most of this production takes place in the United States and Israel.

The history of its discovery involves two chemists working almost at the same time. In 1825, Carl Jacob Löwig isolated bromine from a mineral water spring in Bad Kreuznach. He used a solution saturated with chlorine and extracted the bromine using diethyl ether.

Antoine Jérôme Balard 1870s
Antoine Jérôme Balard 1870s

Shortly after, in 1826, Antoine Jérôme Balard discovered it independently. He found bromine chemicals in the ash of seaweed from the salt marshes of Montpellier. Balard initially called the substance "muride," from the Latin word for brine. Eventually, the name was changed to bromine. This name comes from the Greek word "bromos," which means stench. This refers to the sharp, pungent odor of its vapors.

Bromine has many important industrial and scientific uses. One of its most significant roles is as a fire retardant.

Tetrabromobisphenol A
Tetrabromobisphenol A

When organobromine compounds are exposed to high heat, they dissociate to release free bromine atoms. This process stops chemical chain reactions that fuel fires. More than half of the bromine produced worldwide each year is used for this purpose. Bromine is also used in photographic film, which relies on silver bromide.

Bromid stříbrný
Bromid stříbrný

It is also used in well drilling fluids and as an intermediate in making organic chemicals.

In the field of medicine, bromine has a complex history. In the late 19th and early 20th centuries, potassium bromide and sodium bromide were used as sedatives. They worked by having inhibitory effects on the central nervous system. While they were eventually replaced by shorter-acting drugs, they are still used in niche roles as antiepileptics. However, large amounts of bromide salts can be toxic to humans. This toxicity can lead to a condition known as bromism.

GHS-pictogram-skull
GHS-pictogram-skull

On a biological level, bromine is also beneficial. It is an essential trace element for collagen development in all animals. It is also helpful for human eosinophils.

Finally, the use of bromine has environmental consequences. In the atmosphere, ultraviolet sunlight can cause volatile organobromine compounds to dissociate.

N-Bromosuccinimide
N-Bromosuccinimide

This releases free bromine atoms that contribute to ozone depletion. Because of this effect, certain compounds like the pesticide methyl bromide are no longer used. This illustrates how a highly reactive and useful element must be managed carefully to protect the Earth's atmosphere.

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🖼️ Images & Media (15)
File:Orthorhombic.svg
Orthorhombic.svg
File:2-Octyl 4-bromo-3-oxobutanoate.svg
2-Octyl 4-bromo-3-oxobutanoate.svg
File:GHS-pictogram-acid.svg
GHS-pictogram-acid.svg
File:GHS-pictogram-pollu.svg
GHS-pictogram-pollu.svg
File:GHS-pictogram-skull.svg
GHS-pictogram-skull.svg
File:N-Bromosuccinimide.svg
N-Bromosuccinimide.svg
File:NFPA 704.svg
NFPA 704.svg
File:Tetrabromobisphenol A.svg
Tetrabromobisphenol A.svg
File:35 (Br I) NIST ASD emission spectrum.png
35 (Br I) NIST ASD emission spectrum.png
File:Bromine vial in acrylic cube.jpg
Bromine vial in acrylic cube.jpg
File:Alkene-bromine-addition-2D-skeletal.png
Alkene-bromine-addition-2D-skeletal.png
File:Bromo-Seltzer Tower MD2.jpg
Bromo-Seltzer Tower MD2.jpg

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