Bromine Br

Discovery

Bromine was discovered twice, almost simultaneously. In 1826 Antoine-Jérôme Balard, a young pharmacist in Montpellier, passed chlorine through the bitter residue of salt-marsh brine and obtained a red-brown liquid, which he reported as a new element.

In Germany, Carl Löwig had isolated the same substance around 1825 from mineral spring water near his hometown of Bad Kreuznach, but Balard's paper appeared before Löwig published. Balard is therefore usually credited with the discovery.

In the mid-nineteenth century potassium bromide became a widely used sedative and one of the first effective anti-epileptic drugs. In the twentieth century, bromine use grew enormously for leaded petrol additives and the fumigant methyl bromide, though environmental concerns later curtailed many of these applications.

Origin of the name

The name comes from the Greek bromos, meaning "stench", a fair description of its odour. The symbol is Br.

Main uses

• Flame retardants: bromine compounds interrupt the chain reactions in flames and are added to electronics housings, insulation foams and textiles, although some persistent types are now restricted internationally.
• Drilling and water treatment: dense calcium and zinc bromide brines are used as clear drilling fluids, and bromine-based disinfectants treat pools and hot tubs.
• Chemicals and pharmaceuticals: bromine is a versatile intermediate in making drugs and agrochemicals.
• Photography: silver bromide was the light-sensitive material in photographic film.

Isotopes

Bromine has two stable isotopes, bromine-79 (about 50.7%) and bromine-81 (about 49.3%), in almost equal amounts. As a result, a molecule containing one bromine atom shows two mass-spectrum peaks two units apart and of nearly equal height, a pattern chemists recognise at a glance. The radioactive isotope bromine-82, with a half-life of about 35 hours, is used as a tracer in hydrology studies.

In everyday life

Commercial bromine comes mainly from bromide-rich brines such as those of the Dead Sea and underground brines in Arkansas. Seawater contains about 65 milligrams per litre.

Liquid bromine causes severe burns on skin, and its vapour strongly irritates the eyes and lungs, so it is handled in fume hoods with protective gear. Methyl bromide, once a common soil and grain fumigant, depletes the ozone layer and has been largely phased out under the Montreal Protocol.

The prized ancient dye Tyrian purple, obtained from sea snails, is itself a bromine compound.