Bromine is a chemical element with the symbol "Br", and atomic number of 35. It is in the halogen group (17). The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826. Elemental bromine is a fuming red-brown liquid at room temperature, corrosive and toxic, with properties between those of chlorine and iodine. Free bromine does not occur in nature, but occurs as colorless soluble crystalline mineral halide salts, analogous to table salt.
Bromine is rarer than about three-quarters of elements in the Earth's crust; however, the high solubility of bromide ion has caused its accumulation in the oceans, and commercially the element is easily extracted from brine pools, mostly in the United States, Israel and China. About 556,000 tonnes were produced in 2007, an amount similar to the far more abundant element magnesium.
At high temperatures, organ obromine compounds readily convert to free bromine atoms, a process which has the effect of stopping free radical chemical chain reactions. This effect makes organobromine compounds useful as fire retardants; more than half the bromine produced industrially worldwide each year is put to this use. Unfortunately, the same property causes sunlight to convert volatile organobromine compounds to free bromine atoms in the atmosphere, and an unwanted side effect of this process is ozone depletion. As a result, many organobromide compounds that were formerly in common use—such as the pesticide methyl bromide—have been abandoned. Bromine compounds are still used for certain purposes, however, including in well-drilling fluids, in film photography, and as an intermediate in the manufacture of organic chemicals.
Bromine has no essential function in mammals, though it is preferentially used over chlorine by one antiparasitic enzyme in the human immune system. Organobromides are needed and produced enzymatically from bromide by some lower life forms in the sea, particularly algae, and the ash of seaweed was one source of bromine's discovery. 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 being replaced by shorter-acting drugs. They retain niche uses as antiepileptics.
Both strontium and strontianite are named after Strontian, a village in Scotland near which the mineral was first discovered in 1790 by Adair Crawfordand William Cruickshank. The production of sugar from sugar beet was in the 19th century the largest application. Strontium compounds are today mostly used for the production of cathode ray tubes. The displacement of cathode ray tubes by other display methods in television sets is changing the overall consumption.
