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The molecule
Two bromine atoms sharing a single bond: a dark red liquid that fumes at room temperature, one of only two elements that do.
Reactive, though less so than chlorine. Aluminum foil dropped into it bursts into flame, and phosphorus ignites. It adds across carbon–carbon double bonds without any heat or catalyst, and the orange color vanishes as it does, which makes bromine water the standard test for an unsaturated compound. It displaces iodine from iodide salts and is itself displaced by chlorine.
Chlorine gas is bubbled through acidified seawater or brine; it oxidizes the bromide to bromine, which is blown out of the solution with air or steam and condensed. The United States (Arkansas brines), Israel and Jordan (the Dead Sea) and China produce most of it.
Flame retardants for plastics and electronics take the largest share. Dense bromide brines are pumped into oil wells to control pressure while drilling. Silver bromide was the light-sensitive layer in photographic film for a century. Bromine compounds also serve as pool sanitizers, in pharmaceuticals and in dyes.
Corrosive. Liquid bromine burns skin slowly and deeply, and the vapor damages eyes and lungs at low concentrations. It is stored in glass with Teflon-lined caps and handled in a fume hood with thick gloves, with a bottle of sodium thiosulfate solution nearby to neutralize spills.