June 5, 2012, 5:39 pm
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Molybdenum disulfide. Source: CC-BY-SA-3.0 Creative Commons

caption Wulfenite. (Source:Mineral Information Institute)

Molybdenum is a metallic, silvery-white element, with an atomic number of 42. Its chemical symbol is Mo. Chemically, it is very stable, but it will react with acids. The physical characteristic that makes molybdenum unique is that it has a very high melting point at 4,730 degrees Fahrenheit. This is 2000 degrees higher than the melting point of steel. It is 1,000 degrees higher than the melting temperature of most rocks. It has the fifth highest melting point of all of the elements.






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Next Element: Technetium


Physical Properties
Color silvery-white
Phase at Room Temp. solid
Density (g/cm3) 10.28
Hardness (Mohs) ---
Melting Point (K) 2890.2
Boiling Point (K) 4923
Heat of Fusion (kJ/mol) 27.6
Heat of Vaporization (kJ/mol) 590
Heat of Atomization (kJ/mol) 658
Thermal Conductivity (J/m sec K) 138
Electrical Conductivity (1/mohm cm) 192.308
Source Molybdenite (sulfide)
Atomic Properties
Electron Configuration [Kr]5s14d5
Number of Isotopes 36 (7 natural)
Electron Affinity (kJ/mol) 72
First Ionization Energy (kJ/mol) 684.9
Second Ionization Energy (kJ/mol) 1588.2
Third Ionization Energy (kJ/mol) 2620.5
Electronegativity 2.24
Polarizability (Å3) 12.8
Atomic Weight 95.94
Atomic Volume (cm3/mol) 9.3
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) ---
Atomic Radius (pm) 139
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) ---
Ionic Radius3+ (pm) 83
Common Oxidation Numbers +4, +6
Other Oxid. Numbers -2, -1, +1, +2, +3, +5
In Earth's Crust (mg/kg) 1.2x100
In Earth's Ocean (mg/L) 1.0x10-2
In Human Body (%) 0.000007%
Regulatory / Health
CAS Number 7439-98-7
OSHA Permissible Exposure Limit (PEL) TWA: 15 mg/m3
OSHA PEL Vacated 1989 TWA: 10 mg/m3
NIOSH Recommended Exposure Limit (REL) IDLH: 5000 mg/m3
University of Wisconsin General Chemistry
Mineral Information Institute
Jefferson Accelerator Laboratory


In biology

The majority of molybdenum molecules or salts have low aqueous solubility, but the molybdate ion MoO42− is somewhat soluble and will form if molybdenum-containing minerals are in contact with oxygen and water. Recent theories suggest that oxygen respiration (release) by early lifeforms was important in removing molybdenum from minerals into a soluble form in the early oceans, where it was used as a catalyst by single-celled organisms. This chain of events may have been key in the history of life, because molybdenum-containing enzymes then became significant cellular catalysts employed by certain bacteria to break molecular nitrogen, permitting biological nitrogen fixation. This, in turn allowed biologically driven nitrogen-fertilization of the oceans, and thus the development of more complex organisms.

More than fifty molybdenum-containing enzymes have been identified in bacteria and animals, even though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Due to the diverse functions of some of the molybdenum enzymes, molybdenum is an essential trace nutrient for life in higher organisms, but not in all bacteria.







The two largest uses of molybdenum are as an alloy in stainless steels and in alloy steels-these two uses consume about 60% of the molybdenum needs in the United States. Stainless steels have the strength and corrosion-resistant requirements for water distribution systems, food handling equipment, chemical processing equipment, home, hospital, and laboratory requirements. Alloy steels include the stronger and tougher steels needed to make automotive parts, construction equipment, and gas transmission pipes.

Other major uses as an alloy include: Tool steels, for things like bearings, dies, and machining components; cast irons, for steel mill rolls, auto parts, and crusher parts; super alloys for use in furnace parts, gas turbine parts, and chemical processing equipment.



Substitutes and Alternative Sources


Further Reading







Institute, M. (2012). Molybdenum. Retrieved from http://www.eoearth.org/view/article/154667


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