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. 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 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 MoO2−4 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 an iron-molybdenum cofactor FeMoco, which is believed to contain either Mo(III) or Mo(IV). 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. The variety of crucial reactions catalyzed by these latter enzymes means that molybdenum is an essential element for all higher eukaryote organisms, including humans.

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Atomic properties

Standard atomic weight95.95 ±0.01
Atomic mass95.951 u

Atomic radii

Radius (empirical)139 pm
Radius (calculated)190 pm
Covalent radius154 ±5 pm

Atomic shell

Electron configurationKr 4d5 5s1
Ionization energy(1st) 7.09243 eV
(2nd) 16.16 eV
(3rd) 27.13 eV
(4th) 40.33 eV
(5th) 54.417 eV
Shell model

Physical properties

Density10.28 g·cm−3 (293.1 K)
Molar volume9.38·10-6 m3·mol−1
Speed of sound6,190 m·s−1


Melting point2,896 K
Boiling point4,912 K
Liquid range2,016 K
Transition temperature0.92 K


Melting enthalpy36 kJ·mol-1
Enthalpy of vaporization600 kJ·mol-1
Binding energy659 kJ·mol-1

Heat and conductivity

Thermal conductivity139 W·m-1·K-1
Expansion coefficient4.8·10-6 K-1


Mohs hardness5.5
Brinell hardness1,500 NM·m-2
Vickers hardness1,530 NM·m-2

Elastic properties

Young’s modulus329 GPa
Shear modulus20 GPa
Bulk modulus230 GPa
Poisson’s ratio0.31

Electrical properties

Electrical conductivity1.82·107 S·m-1
Resistance5.5·10-8 Ωm


Magnetic susceptibility8.9·10-5 cm3·mol−1 (298 K)

Optical properties

Reflectivity58 %

Chemical properties

Basicitystrongly acidic
Oxidation state2, 3, 4, 5, 6
Standard potential-0.152 V (MoO2 + 4e- + 4H+ → Mo + 2H2O)


Pauling scale2.16
Sanderson scale1.15
Allred-Rochow scale1.3
Ghosh-Gupta scale3.099 eV
Nagle scale1.26
Pearson absolute negativity3.9 eV

Other properties

Natural occurrenceprimordial
Crystal structureBody-centered cubic
Goldschmidt Classificationsiderophile
Superconductorwith transition tempperature (solid body, normal pressure)
Price/kg40.1 USD

Natural abundances

5 ppb ≈ 5.02·1010 M☉
9 ppb ≈ 1.79·1010 Mt
1,200 ppb ≈ 1.2 g
Earth’s crust
1,100 ppb ≈ 30,400 Mt
10 ppb ≈ 13.7 Gt
Flowing water
0.8 ppb ≈ 12.8 kt
Human body
100 ppb ≈ 7 mg