Rhodium - chemistry.

Rhodium - chemistry. Rhodium (Greek rhodon, "rose"), symbol Rh, brilliant silvery white metallic element used principally in alloys. Rhodium is one of the transition elements of the periodic table (see Periodic Law). The atomic number of rhodium is 45. Rhodium was discovered in 1803 by the British chemist William Hyde Wollaston. Rhodium metal is very durable. It is insoluble in ordinary acids and is very difficult to fuse. It has a hardness of 4. The compounds of rhodium span oxidation states of 1 to 6. Aqueous solutions of many of its salts are rose colored, from which its name is derived. The metal occurs as an alloy in platinum ores, in osmiridium, and in gold-rhodium ores called rhodite. Very tiny amounts of rhodium occur in some nickel ores, and most commercially obtained rhodium is a by-product of nickel production. Of the elements in the Earth's crust, rhodium ranks about 81st in order of abundance. The element melts at about 1966°C (about 3571°F), boils at about 3695°C (about 6683°F), and has a specific gravity of 12.4. The atomic weight of rhodium is 102.905. Rhodium is used mostly as an alloy with platinum; the resulting alloy has the desirable properties of platinum and is also hard and durable. Rhodium-platinum alloys are used in thermocouples, measuring high temperatures. Pure rhodium is used as a mirror surface in searchlights and as a plating finish for jewelry and silverware. Rhodium black is a finely divided metal that contains some oxide and hydride. It is used both as a catalyst and as a black pigment for porcelain ware. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.