Molybdenum

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Molybdenum,  42Mo
IMAG0137.jpg
General properties
Name, symbol Molybdenum, Mo
Appearance Silvery-gray metal
Molybdenum in the periodic table
Cr

Mo

W
NiobiumMolybdenumTechnertium
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
Silvery-gray
Phase 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  9.33 g/cm3
Heat of fusion 37.48 kJ/mol
Heat of 598 kJ/mol
Molar heat capacity 24.06 J/(mol·K)
 pressure
Atomic properties
Oxidation states 6, 5, 4, 3, 2, 1, −1, −2, −4 ​(a strongly acidic oxide)
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
Miscellanea
Crystal structure ​​body-centered cubic (bcc)
Speed of sound thin rod 5400 m/s (at )
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) (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
History
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.

Properties

Chemical

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

Physical

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.

Availability

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.

Isolation

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

MoO3 + 3 H2 → Mo + 3 H2O

Projects

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

Handling

Safety

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.

Storage

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

Disposal

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

References

Relevant Sciencemadness threads