bromide, any of a group of compounds that contain bromine and a more electropositive element or radical. Bromides are formed by the reaction of bromine or a bromide with another substance; they are widely distributed in nature. Most metal bromides are water soluble; exceptions are bromides of copper, lead, mercury, and silver that are very slightly soluble in water. Potassium bromide, KBr, and sodium bromide, NaBr, are the familiar bromides used in medicine as sedatives; they should be used under a doctor's direction since they are habit-forming. Magnesium bromide, found in seawater, is a source of pure bromine. Silver bromide is one of the light-sensitive silver salts used in films, plates, and printing papers for photography. Hydrobromic acid is a water solution of hydrogen bromide, a gas. The presence of a bromide in a water solution can be detected by adding chlorine and carbon disulfide, CS2; the bromine is displaced from its compound and dissolves in the CS2, giving it a characteristic orange color.