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Chemical element, symbol Mo and atomic number 42 / From Wikipedia, the free encyclopedia

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Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin molybdaenum, which is based on Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores.[7] 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.[8]

Quick facts: Molybdenum, Pronunciation, Appearance, Standa...
Molybdenum, 42Mo
Pronunciation/məˈlɪbdənəm/ (mə-LIB-də-nəm)
Appearancegray metallic
Standard atomic weight Ar°(Mo)
  • 95.95±0.01
  • 95.95±0.01 (abridged)[1]
Molybdenum in the periodic table


Atomic number (Z)42
Groupgroup 6
Periodperiod 5
Block  d-block
Electron configuration[Kr] 4d5 5s1
Electrons per shell2, 8, 18, 13, 1
Physical properties
Phase at STPsolid
Melting point2896 K (2623 °C, 4753 °F)
Boiling point4912 K (4639 °C, 8382 °F)
Density (near r.t.)10.28 g/cm3
when liquid (at m.p.)9.33 g/cm3
Heat of fusion37.48 kJ/mol
Heat of vaporization598 kJ/mol
Molar heat capacity24.06 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2742 2994 3312 3707 4212 4879
Atomic properties
Oxidation states−4, −2, −1, 0, +1,[2] +2, +3, +4, +5, +6 (a strongly acidic oxide)
ElectronegativityPauling scale: 2.16
Ionization energies
  • 1st: 684.3 kJ/mol
  • 2nd: 1560 kJ/mol
  • 3rd: 2618 kJ/mol
Atomic radiusempirical: 139 pm
Covalent radius154±5 pm
Color lines in a spectral range
Spectral lines of molybdenum
Other properties
Natural occurrenceprimordial
Crystal structure body-centered cubic (bcc)
Body-centered cubic crystal structure for molybdenum
Speed of sound thin rod5400 m/s (at r.t.)
Thermal expansion4.8 µm/(m⋅K) (at 25 °C)
Thermal conductivity138 W/(m⋅K)
Thermal diffusivity54.3 mm2/s (at 300 K)[3]
Electrical resistivity53.4 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[4]
Molar magnetic susceptibility+89.0×10−6 cm3/mol (298 K)[5]
Young's modulus329 GPa
Shear modulus126 GPa
Bulk modulus230 GPa
Poisson ratio0.31
Mohs hardness5.5
Vickers hardness1400–2740 MPa
Brinell hardness1370–2500 MPa
CAS Number7439-98-7
DiscoveryCarl Wilhelm Scheele (1778)
First isolationPeter Jacob Hjelm (1781)
Isotopes of molybdenum
Main isotopes[6] Decay
abun­dance half-life (t1/2) mode pro­duct
92Mo 14.7% stable
93Mo synth 4×103 y ε 93Nb
94Mo 9.19% stable
95Mo 15.9% stable
96Mo 16.7% stable
97Mo 9.58% stable
98Mo 24.3% stable
99Mo synth 65.94 h β 99mTc
100Mo 9.74% 7.1×1018 y ββ 100Ru
Symbol_category_class.svg Category: Molybdenum
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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 grey cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of the 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−
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 an iron-molybdenum cofactor FeMoco, which is believed to contain either Mo(III) or Mo(IV).[9][10] This is distinct from the fully oxidized Mo(VI) found complexed with molybdopterin in all other molybdenum-bearing enzymes, which perform a variety of crucial functions.[11] The variety of crucial reactions catalyzed by these latter enzymes means that molybdenum is an essential element for all higher eukaryote organisms, including humans.