Bromine is one of the only liquid nonmetals at room temperature, with a density of about 3.1028 g/cm³ and a melting point around −7 °C; it is deep red-brown, highly volatile, sharply pungent, and highly toxic. It is extracted mainly from bromides in seawater, enriched by air-blowing or resin processes before conversion into downstream products. Brominated flame retardants are bromine's largest industrial outlet: bromine compounds release bromine radicals that trap combustion chain reactions during burning, widely used in electronics enclosures, building insulation foams, textiles, and automotive interiors, and are an important means of plastics flame retardancy. In dyes and pharmaceuticals, bromine is used to synthesize indigo, disperse dyes, and numerous pharmaceutical intermediates; seawater bromine extraction itself is also a major branch of the marine chemical industry. Historically silver bromide was the core photosensitive material of photographic film, but has shrunk sharply in the digital era. It must be stressed that elemental bromine and its vapor are highly toxic and corrosive, so handling must be done sealed inside a fume hood.
Sodium bromide NaBr was once used as a sedative; today it mainly serves in oil drilling muds, water treatment, and as a bromide feedstock. Silver bromide AgBr is the photosensitive material of traditional photographic film and paper, decomposing under light to form silver grains that make a latent image; demand has fallen sharply with digital photography but it still survives in specialty films. Potassium bromide KBr is transparent to infrared light and has long served as sample windows and pressed pellets in infrared spectrometry. Lithium bromide LiBr is highly water-soluble and strongly hygroscopic, and is the working fluid of absorption chillers, using waste heat to drive large air-conditioning and refrigeration systems. Brominated flame retardants such as decabromodiphenylethane and tetrabromobisphenol A are the workhorses of plastics and textile flame retardancy. Methyl bromide CH3Br was once a widely used soil fumigant insecticide, phased out under international treaty because it depletes the ozone layer. Hydrobromic acid HBr is used in pharmaceuticals, dyes, and catalyst synthesis.
