Molybdenum News Center

A chemical element, Mo, atomic number 42, and atomic weight 95.94, in the periodic table in the triad of transition elements that includes chromium (atomic number 24) and tungsten (atomic number 74). Research has revealed it to be one of the most versatile chemical elements, finding applications not only in metallurgy but also in paints, pigments, and dyes; ceramics; electroplating; industrial catalysts; industrial lubricants; and organometallic chemistry. Molybdenum is an essential trace element in soils and in agricultural fertilizers. Molybdenum atoms have been found to perform key functions in enzymes (oxidases and reductases), with particular interest being directed toward its role in nitrogenase, which is employed by bacteria in legumes to convert inert nitrogen (N2) of the air into biologically useful ammonia (NH3). 

 

Molybdenum is widely distributed in the Earth's crust at a concentration of 1.5 parts per million by weight in the lithosphere and about 10 parts per billion in the sea. It is found in at least 13 minerals, mainly as a sulfide [molybdenite (MoS2)] or in the form of molybdates [for example, wulfenite (PbMoO4) and magnesium molybdate (MgMoO4)].

 

Although molybdenum is closer to chromium in atomic weight and atomic number, its chemical behavior is usually very similar to that of tungsten, which has nearly the same atomic radius. (This is due to the so-called lanthanide contraction in which atomic radii decrease for elements 57 to 71 found in the period between molybdenum and tungsten.) See also Chromium; Lanthanide contraction; Tungsten.

 

Molybdenum atoms contain six valence electrons (4d55s1), which are employed with great versatility in forming compounds and complexes in which electronic configurations vary from d0 (no d electrons in oxidation state + 6) to d8 (8 d electrons in oxidation state 2). The +6 state is preferred, but all states from 2 to +6 are known. States usually exhibit a variety of coordination numbers (4 to 9), and include polynuclear complexes and metal-metal bonds in metallic clusters with two to six metal atoms in their metallic cores. 

Molybdenum forms a very large number of compounds with oxygen. Low-valent molybdenum [for example, Mo(CO)6 and Mo2, Mo3, and Mo6 clusters] has a very rich organometallic chemistry, including clusters that are being studied as models for molybdenum metal surfaces that catalyze organic reactions employed in industrial syntheses and oil refining. The ability of molybdenum atoms to vary oxidation state, coordination number, and coordination geometry and to form metal-metal bonds in clusters accounts in part for the large number of industrial catalysts and biological enzymes in which Mo atoms are found at the active site for catalysis. See also Chemical bonding; Coordination chemistry; Electron configuration.

 

Molybdenum is a high-melting silver-gray metal, strong even at high temperatures, hard, and resistant to corrosion (see table). It also exhibits high conductivity, a high modulus of elasticity, high thermal conductivity, and a low coefficient of expansion. Its major use is in alloy steels, for example, as tool steels (≤10% molybdenum), stainless steel, and armor plate. Up to 3% molybdenum is added to cast iron to increase strength. Up to 30% molybdenum may be added to iron-, cobalt-, and nickel-based alloys designed for severe heat- and corrosion-resistant applications. It may be used in filaments for light bulbs, and it has many applications in electronic circuitry. 

 

 

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