chloride (klōrˈĪd, klôrˈ–) [key], chemical compound containing chlorine. Most chlorides are salts that are formed either by direct union of chlorine with a metal or by reaction of hydrochloric acid (a water solution of hydrogen chloride) with a metal, a metal oxide, or an inorganic base. Chloride salts include sodium chloride (common salt), potassium chloride, calcium chloride, and ammonium chloride. Most chloride salts are readily soluble in water, but mercurous chloride (calomel) and silver chloride are insoluble, and lead chloride is only slightly soluble. Some chlorides, e.g., antimony chloride and bismuth chloride, decompose in water, forming oxychlorides. Many metal chlorides can be melted without decomposition; two exceptions are the chlorides of gold and platinum. Most metal chlorides conduct electricity when fused or dissolved in water and can be decomposed by electrolysis to chlorine gas and the metal. Chlorine forms compounds with the other halogens and with oxygen; when chlorine is the more electronegative element in the compound, the compound is called a chloride. Thus, compounds with bromine and iodine are bromine chloride, BrCl, and iodine chloride, ICI, but compounds with oxygen or fluorine (which are more electronegative than chlorine) are oxides (e.g., chlorine dioxide, ClO2) or fluorides (e.g., chlorine fluoride, ClF) respectively. Many organic compounds contain chlorine, as is indicated by common names such as carbon tetrachloride, methylene chloride, and methyl chloride. However, in the nomenclature system for organic chemistry adopted by the International Union of Pure and Applied Chemistry (IUPAC), the presence in a compound of chlorine bonded to a carbon atom is indicated by the prefix or infix chloro; thus, carbon tetrachloride is tetrachloromethane, methylene chloride is dichloromethane, and methyl chloride is chloromethane.