Difference between revisions of "Molybdenum"

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Revision as of 16:33, 1 March 2016

Molybdenum,  42Mo
General properties
Name, symbol Molybdenum, Mo
Appearance Silvery-gray metal
Molybdenum in the periodic table


Atomic number 42
Standard atomic weight (Ar) 95.95(1)
Group, block VI; d-block
Period period 5
Electron configuration [Kr] 4d5 5s1
per shell
2, 8, 18, 13, 1
Physical properties
Phase Solid
Boiling point 4912 K ​(4639 °C, ​​8382 °F)
Density near r.t. 10.28 g/cm3
when liquid, at  9.33 g/cm3
Heat of fusion 37.48 kJ/mol
Heat of 598 kJ/mol
Molar heat capacity 24.06 J/(mol·K)
Atomic properties
Electronegativity Pauling scale: 2.16
energies 1st: 684.3 kJ/mol
2nd: 1560 kJ/mol
3rd: 2618 kJ/mol
Atomic radius empirical: 139 pm
Covalent radius 154±5 pm
Crystal structure ​​body-centered cubic (bcc)
Speed of sound thin rod 5400 m/s (at )
Thermal conductivity 138 W/(m·K)
Thermal diffusivity 54.3 mm2/s (at 300 K) (at 300 K)
Electrical resistivity 53.4 Ω·m (at 20 °C)
Magnetic ordering Paramagnetic
Young's modulus 329 GPa
Shear modulus 126 GPa
Bulk modulus 230 GPa
Poisson ratio 0.31
Mohs hardness 5.5
Vickers hardness 1400–2740 MPa
Brinell hardness 1370–2500 MPa
CAS Registry Number 7439-98-7
Discovery Carl Wilhelm Scheele (1778)
First isolation Peter Jacob Hjelm (1781)
· references

Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, which in turn is from Ancient Greek molybdos (Μόλυβδος), meaning "lead", since its ores were confused with lead ores.



Molybdenum is resistant to most form of corrosion. Weak oxidation of molybdenum begins at 300 °C, with bulk oxidation occurring at over 600 °C. Molybdenum trioxide is the main oxide that forms:

2 Mo + 3 O2 → 2 MoO3


Molybdenum is a very hard silvery-grey metal, with a Mohs hardness of 5.5. It has a high melting point, of 2,623 °C and a boiling point of 4639 °C. It is quite dense, with a density of 10.28 g/cm3. It has the second lowest coefficients of thermal expansion after pure tungsten among the metals.


Molybdenum is sold by various chemical suppliers and metal companies.

Is is also found in many molybdenum steels, which is used for various tools.

The support wiring that holds the tungsten filament in light bulbs is made of molybdenum. Likewise, the bridge that connects the tungsten filament to the the electric wiring in certain light bulbs, like the car ones is made of molybdenum. However, one would need a huge amount of light bulbs to obtain a useful amount of molybdenum.


Molybdenum metal can be made by reducing molybdenum trioxide with hydrogen at high temperatures.

MoO3 + 3 H2 → Mo + 3 H2O


  • Make molybdenum trioxide
  • Make sodium molybdate
  • Grow crystals (molybdenum crucibles)



Molybdenum has low reactivity and thus is not toxic for the organism. Direct contact with molybdenum does not cause dermatitis. Molybdenum is an essential trace element and crucial for the survival of animals.

The most important role of molybdenum in living organisms is as a metal heteroatom at the active site in various enzymes, most notably in nitrogen fixation, process encountered in certain bacteria.

However, molybdenum fumes and compounds are known to display toxicity and should be candled with care. Molybdenum halides hydrolyze in contact with moist air, releasing corrosive fumes of hydrochloric acid.


Molybdenum does not require special storage and can be stored in any container.


Molybdenum and its compounds display little toxicity and can be dumped in trash.


Relevant Sciencemadness threads