Occurrence The element molybdenum (from the Greek molybdos , meaning "lead-like") is not found free in nature . The main commercial source of molybdenum is the mineral molybdenite (MoS 2 ), but it is also found in minerals such as wulfenite ( Pb Mo O 4 ) and powellite ( Ca MoO 4 ).
Molybdenum is obtained by mining molybdenite directly and is also recovered as a byproduct of copper mining. Molybdenum is present in ores from 0.01 percent to about 0.5 percent. About half of the world's molybdenum is mined in the United States . The Russian Luna 24 mission discovered a single grain (1 × 0.6 micrometer) of pure molybdenum in a pyroxene fragment taken from Mare Crisium on the Moon . History Until the late eighteenth century, the compounds of molybdenum were confused with those of other elements, such as carbon or lead . In 1778, Carl Wilhelm Scheele was able to determine that molybdenum was separate from graphite and lead, and he isolated the oxide of the metal from molybdenite. In 1782, Hjelm isolated an impure extract of the metal by reducing the oxide with carbon. Molybdenum was little used and remained in the laboratory until the late nineteenth century. Subsequently, a French company (Schneider and Co.) tried molybdenum as an alloying agent in steel armor plating and noted its usefulness as a hardener of steel. Molybdenum use soared during World War I , when the increased demand for tungsten made that element scarce and high-strength steels were at a premium. Notable characteristics Molybdenum is a transition metal that lies in period five of the periodic table , between niobium and technetium . In addition, it is located in group six (former group 6B), between chromium and tungsten . Pure molybdenum has a melting point of 2623°C, which is among the highest melting points of all elements. The pure metal has a tendency to flake apart during machining, but it is useful as an additive that hardens steel . Isotopes Molybdenum has six stable isotopes and many radioisotopes , most of which have very short half-lives . Mo-99 is used to create Tc-99 for the nuclear isotope industry. Compounds Ammonium tetrathiomolybdate ((NH 4 ) 2 MoS 4 ): This bright red ammonium salt is an important reagent in the chemistry of molybdenum and has been used as a building block in bioinorganic chemistry . The thiometallate anion (MoS 4 -2 ) has the distinctive property of undergoing oxidation at the sulfur centers, concomitant with reduction of the metal from Mo(VI) to Mo(IV). Molybdic acid : It refers to hydrated forms of molybdenum trioxide. The simplest form is the monohydrate, H 2 MoO 4 , but the dihydrate is also found. The salts of molybdic acid are called molybdates. As molybdenum can have various oxidation states , it can form a wide variety of salts.
Sodium molybdate (Na 2 MoO 4 ): It is often found as the dihydrate (Na 2 MoO 4 . 2H 2 O) and is useful as a source of molybdenum. It is also used in biochemistry and medicinal chemistry to track various colorless organic chemicals that, in the presence of the salt, can be stained blue. The blue color, also called molybdenum blue, is a complex of molybdates (Mo(VI), Mo(V)).
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- Fall '19
- Peter Jacob Hjelm