Molybdenum - chemistry.

Molybdenum - chemistry. Molybdenum, symbol Mo, metallic element with chemical properties similar to those of chromium. Molybdenum is one of the transition elements of the periodic table (see Periodic Law). The atomic number of molybdenum is 42. Molybdenum was discovered in 1778 by the Swedish chemist Carl Wilhelm Scheele. The element's name come from the Greek word molybdos, meaning lead; the two metals had previously been confused. Molybdenum is a silvery white, tough, malleable metal. Molybdenum is dissolved by dilute nitric acid and aqua regia, and is attacked by fused alkalies; it is not attacked by air at ordinary temperatures, but at elevated temperatures it oxidizes to form molybdenum oxide. Molybdenum melts at about 2623°C (about 4753°F), boils at about 4640°C (about 8380°F), and has a specific gravity, or relative density, of 10.2. Molybdenum does not occur free in nature, but in the form of its ores, the most important of which are molybdenite and wulfenite. It ranks 56th in order of abundance of the elements in Earth's crust and is an important trace element in soils, where it contributes to the growth of plants. The metal is used chiefly in alloying steel. The alloy withstands high temperatures and pressures and is very strong, making it useful for structural work, aircraft parts, and forged automobile parts. Molybdenum wire is used in electron tubes, and the metal also serves as electrodes in glass furnaces. Molybdenum sulfide is used as a lubricant in environments requiring high temperatures. About two-thirds of the world supply of the metal is obtained as a byproduct of copper mining, with the United States the single largest producer, followed by Canada. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.