Bromine

Bromine is the chemical element with atomic number 35 and the symbol Br. It is a halogen in group 17 of the periodic table and a deep-red, oily liquid at room temperature, with a sharp smell. Its compounds are used in flame retardants, fire-extinguishing agents, agricultural chemicals and pharmaceuticals.

History of bromine

Bromine was identified in the 1820s by two chemists working independently. Antoine-Jérôme Balard was studying salty water from Montpellier, France. He took the concentrated residue left after most of the brine had evaporated and passed chlorine gas through it, which released an orange-red liquid. Balard concluded that it was a new element and sent an account of his findings to the journal of the French Academy in 1826.

A year earlier, Carl Löwig, a student at Heidelberg, had prepared bromine from the water of a natural spring and given a sample to his professor. Löwig was asked to make more of it, and while he was doing so Balard published his results. Balard therefore became known as the discoverer, although the Royal Society of Chemistry credits both men.

The name comes from the Greek word bromos, meaning stench, a reference to the sharp smell of the liquid and its vapor.

Properties of bromine

The standard atomic weight of bromine is given by NIST, using IUPAC data, as the interval 79.901 to 79.907. It is an interval rather than a single number because the mix of bromine’s two stable isotopes varies slightly between natural samples. The electron configuration is [Ar] 3d10 4s2 4p5, which leaves the outer shell one electron short of full. As a result, bromine tends to gain one electron to form the bromide ion, and its common oxidation states include minus 1, plus 1 and plus 5.

Bromine is a liquid at 20 degrees Celsius. It melts at minus 7.2 degrees Celsius and boils at 58.8 degrees Celsius, so it gives off vapor easily, and its density of about 3.10 grams per cubic centimeter is roughly three times that of water. Like fluorine, the first member of the halogen group, bromine is a nonmetal that reacts readily with many other substances.

PubChem lists a Pauling electronegativity of 2.96, a first ionization energy of 11.814 electronvolts and an electron affinity of 3.365 electronvolts. Electronegativity measures how strongly an atom pulls on shared electrons, and a value near 3 means bromine attracts them strongly. The Royal Society of Chemistry gives an enthalpy of 192.8 kilojoules per mole for the bond between the two atoms of a Br2 molecule, which is the energy needed to split one mole of those bonds. A bromine atom has a covalent radius of 1.17 angstroms and a non-bonded radius of 1.85 angstroms.

Occurrence and production of bromine

Bromine is not found uncombined in nature. It occurs as bromide, the negatively charged ion, dissolved in water, and the Royal Society of Chemistry notes that small amounts of bromide are present in all living things.

Brines are very salty solutions found in underground deposits and salt lakes.

Commercial bromine is extracted by electrolysis from natural brine deposits that are rich in bromide. The United States, Israel and China are named as the main sources. Bromine was the first element to be extracted from seawater, but that route is now economically viable only at the Dead Sea in Israel, where bromide makes up as much as 0.5 percent of the water. For a producer, a richer starting solution means less water to process for each tonne of bromine recovered.

Uses of bromine

Bromine is used to make agricultural chemicals, dyestuffs, insecticides, pharmaceuticals and chemical intermediates, which are compounds that serve as steps in making other products. Some of these uses are being phased out for environmental reasons, but new uses continue to be found.

Bromine compounds are widely used as flame retardants. They are added to furniture foam, the plastic casings of electronics and textiles so that these materials burn less readily. The Royal Society of Chemistry reports that bromine as a flame retardant has been phased out in the United States because of toxicity concerns. Organic bromine compounds also went into halon fire extinguishers systems used to fight fires in places such as museums, aircraft and tanks.

Silver bromide was an important chemical in film photography because it is sensitive to light. Before leaded fuels were phased out, bromine was used to prepare 1,2-dibromoethane, an anti-knock additive that kept engines from igniting fuel too early.

Isotopes of bromine

Isotopes are atoms of the same element that have different numbers of neutrons. Every bromine atom has 35 protons, so bromine-79 has 44 neutrons and bromine-81 has 46 neutrons. Bromine has two stable isotopes. NIST gives the abundance of bromine-79 as 50.69 percent and that of bromine-81 as 49.31 percent, so the two are almost equally common. Because the element is a nearly even mixture of two isotopes, no single mass number dominates, and the atomic weight of about 79.9 falls between 79 and 81. The Royal Society of Chemistry lists bromine-79 as the key isotope.

Health and environmental effects of bromine

Bromine is toxic. According to the Royal Society of Chemistry, it irritates the eyes and throat and produces painful sores when it touches the skin. Bromine has no known biological role in humans, even though bromide is present in small amounts in all living things.

Environmental concerns have shaped how bromine is used. The phase-out of bromine-based flame retardants in the United States and the end of leaded fuels, which removed the market for the anti-knock additive, both reflect changing rules and concerns about health and the environment. This overview is general background and not advice.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue