(So named (Greek rhodon, "rose") by its discoverer, after the color of a dilute solution of its salts) A hard, silvery-white metallic chemical element, one of the platinum metals. Rhodium is the rarest of all metals on Earth. It occurs native with other platinum metals in river sands in North and South America, and as a byproduct of nickel production in copper-nickel sulfide ores of Ontario. The major use of rhodium is as a hardener for platinum and palladium, to produce alloys used for electrodes, furnace windings, crucibles and thermocouples. It is often used as an electrical contact material as it has a low resistance and is highly resistant to corrosion. Rhodium is used in unalloyed form to electroplate optical instruments and silverware, jewelry, and other decorative articles. It is also used as a catalyst. Rhodium is inert to all acids but is attacked by fused alkali metals. It is stable in air up to 600°C.

William Hyde Wollaston discovered rhodium in 1803 in London, England in crude platinum ore from South America. He dissolved the ore in aqua regia, neutralised the acid with sodium hydroxide, and precipitated the platinum by treatment with ammonium chloride, as ammonium chloroplatinate. Palladium was then removed as palladium cyanide by treatment with mercuric cyanide. What remained was a red material containing rhodium chloride salts from which rhodium metal was obtained by reduction with hydrogen gas.

Symbol: Rh
Atomic number: 45
Atomic weight: 102.90550
Density (at room temperature and pressure): 12.4 g/cc
Melting point: 1,966°C
Boiling point: 3,695°C
Main valences: +1, +3
Ground state electron configuration: [Kr]4d85s1