Molybdenum-+Element+number+42

Molybdenum is element number 42, in between niobium and technetium. The name is from Neo-Latin //Molybdaenum//, from Ancient Greek Μόλυβδος //molybdos//, meaning //lead//, since its ores were confused with lead ores. Its pure form has a silvery appearance and has the sixth highest melting point of any element, only surpassed by tantalum, rhenium, osmium, tungsten and carbon. Molybdenum is an important ingredient in enzymes and catalysts. Recent theories suggest that the release of oxygen by early life was important in removing molybdenum from minerals into a soluble form in the early oceans, where it was used as a catalyst by single-celled organisms. This sequence may have been important in the history of life, because molybdenum-containing enzymes then became the most important catalysts used by some bacteria to break the chemical bond in atmospheric molecular nitrogen, allowing biological nitrogen fixation. This, in turn allowed biologically driven nitrogen-fertilization of the oceans, and thus the development of more complex organisms. At least 50 molybdenum-containing enzymes are now known in bacteria and animals, though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Due to the diverse functions of the remainder of the enzymes, molybdenum is a required element for life in higher organisms (eukaryotes), though not in all bacteria.

It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys. Industrially, molybdenum compounds are used in high pressure and high temperature applications, as pigments and catalysts.

__**History**__
 * Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from minerals salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm. Molybdenite ** —the principal ore from which molybdenum is now extracted—was previously known as molybdena. Molybdena was confused with and often implemented as though it were graphite. Like graphite, molybdenite can be used to black a surface or as a solid lubricant. Even when molybdena was distinguishable from graphite, it was still confused with a common lead ore (now called galena), which took its name from Ancient Greek Μόλυβδος //molybdos//, meaning //lead.// Although apparent deliberate alloying of molybdenum with steel in one 14 th century Japanese sword (mfd. ca. 1330) has been reported, that art was never employed widely and was later lost. In 1754, Bengt Andersson Qvist examined molybdenite and determined that it did not contain lead and was thus not the same as galena.

It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized molybdena was neither graphite nor lead.He and other chemists then correctly assumed that it was the ore of a distinct new element, named //molybdenum// for the mineral in which it was discovered. Peter Jacob Hjelm successfully isolated molybdenum using carbon and linseed oil in 1781.

During the WWI, demand for molybdenum spiked; it was used both in armour plating and as a substitute for tungsten in high speed steels. Some British tanks were protected by 75 mm manganese steel plating, but this proved to be ineffective. The manganese steel plates were replaced with 25 mm molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection. After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications. In WWII, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.

The most important use of the molybdenum in living organisms is as a metal heteroatom at the active site in certain enzymes. In nitrogen fixation in certain bacteria, the nitrogenase enzyme, which is involved in the terminal step of reducing molecular nitrogen, usually contains molybdenum in the active site (though replacement of Mo with iron or vanadium is also known). The structure of the catalytic center of the enzyme is similar to that in iron-sulfur proteins: it incorporates a Fe 4 S 3 and multiple MoFe 3 S 3 clusters.
 * __Biological Role__**

In 2008, evidence was reported that a scarcity of molybdenum in the Earth's early oceans was a limiting factor in the further evolution of eukaryotic life (which includes all plants and animals) as eukaryotes cannot fix nitrogen and must acquire it from prokaryotic bacteria. The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. Oxygen dissolved in seawater helps dissolve molybdenum from minerals on the sea bottom. However, although oxygen may promote nitrogen fixation via making molybdenum available in water, it also directly poisons these nitrogenase enzymes, so that organisms which continued to fix nitrogen in aerobic conditions were required to isolate their nitrogen-fixing enzymes in heterocysts, or similar structures.

The human body contains about 0.07 mg of molybdenum per kilogram of weight. It occurs in higher concentrations in the liver and kidneys and in lower concentrations in the vertebrae. Molybdenum is also present within human tooth enamel and may help prevent its decay. Pork, lamb and beef liver each have approximately 1.5 parts per million of molybdenum. Other significant dietary sources include green beans, eggs, sunflower seeds, wheat flour, lentils, cucumbers and cereal grain.

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 * __Reference (that's right, no "s"):__**