Molybdenum is a chemical element with the symbol Mo and atomic number 42. It is a silvery metal having a very high melting point. It is sometimes used as a contact material in reed switches for switching high current loads.
|Standard atomic weight (Ar, standard)||95.95(1)|
|Molybdenum in the periodic table|
|Atomic number (Z)||42|
|Element category||transition metal|
|Electron configuration||[Kr] 4d5 5s1|
Electrons per shell
|2, 8, 18, 13, 1|
|Phase at STP||solid|
|Melting point||2896 K (2623 °C, 4753 °F)|
|Boiling point||4912 K (4639 °C, 8382 °F)|
|Density (near r.t.)||10.28 g/cm3|
|when liquid (at m.p.)||9.33 g/cm3|
|Heat of fusion||37.48 kJ/mol|
|Heat of vaporization||598 kJ/mol|
|Molar heat capacity||24.06 J/(mol·K)|
|Oxidation states||−4, −2, −1, +1, +2, +3, +4, +5, +6 (a strongly acidic oxide)|
|Electronegativity||Pauling scale: 2.16|
|Atomic radius||empirical: 139 pm|
|Covalent radius||154±5 pm|
|Spectral lines of molybdenum|
|Crystal structure||body-centered cubic (bcc)|
|Speed of sound thin rod||5400 m/s (at r.t.)|
|Thermal expansion||4.8 µm/(m·K) (at 25 °C)|
|Thermal conductivity||138 W/(m·K)|
|Thermal diffusivity||54.3 mm2/s (at 300 K)|
|Electrical resistivity||53.4 nΩ·m (at 20 °C)|
|Magnetic susceptibility||+89.0·10−6 cm3/mol (298 K)|
|Young's modulus||329 GPa|
|Shear modulus||126 GPa|
|Bulk modulus||230 GPa|
|Vickers hardness||1400–2740 MPa|
|Brinell hardness||1370–2500 MPa|
|Discovery||Carl Wilhelm Scheele (1778)|
|First isolation||Peter Jacob Hjelm (1781)|
|Main isotopes of molybdenum|
Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.
Molybdenum does not occur naturally as a free metal on Earth; it is found only in various oxidation states in minerals. The free element, a silvery metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of world production of the element (about 80%) is used in steel alloys, including high-strength alloys and superalloys.
Most molybdenum compounds have low solubility in water, but when molybdenum-bearing minerals contact oxygen and water, the resulting molybdate ion MoO2−
4 is quite soluble. Industrially, molybdenum compounds (about 14% of world production of the element) are used in high-pressure and high-temperature applications as pigments and catalysts.
Molybdenum-bearing enzymes are by far the most common bacterial catalysts for breaking the chemical bond in atmospheric molecular nitrogen in the process of biological nitrogen fixation. At least 50 molybdenum enzymes are now known in bacteria, plants, and animals, although only bacterial and cyanobacterial enzymes are involved in nitrogen fixation. These nitrogenases contain molybdenum in a form different from other molybdenum enzymes, which all contain fully oxidized molybdenum in a molybdenum cofactor. These various molybdenum cofactor enzymes are vital to the organisms, and molybdenum is an essential element for life in all higher eukaryote organisms, though not in all bacteria.