Molybdenum Facts – Element Symbol Mo or Number 42


Molybdenum Facts

Molybdenum is a transition metal with element symbol Mo and atomic number 42. It’s notable for its strength, corrosion resistance, and high melting point. You encounter it in daily life as a component of stainless steel and in metal for tools, plus it is an essential trace nutrient.

Discovery and Isolation

Molybdenum was discovered in 1778 by Swedish chemist Carl Wilhelm Scheele, who identified it as a new element in molybdenite ore. However, it was often confused with graphite and lead ore. Peter Jacob Hjelm successfully isolated the pure metal in 1781 by reducing molybdenum trioxide (MoO3) with carbon.

Naming

The element takes its name for the Greek word “molybdos,” meaning lead. The name reflects its resemblance to lead ores.

Appearance and Properties

Molybdenum has a silvery-white metallic appearance and is very hard. It has a high melting point of 2623 °C, good thermal and electrical conductivity, and a low coefficient of thermal expansion. It retains strength at high temperatures, making it ideal for high-heat applications. While the metal resists corrosion, it reacts with hydrogen peroxide and the halogens.

Element Group

Molybdenum is a member of the transition metals. Specifically, it is in group 6 in the periodic table, alongside chromium and tungsten. It shares similar properties with these metals.

Molybdenum Isotopes

Natural molybdenum consists of seven isotopes, with masses of 92, 94, 95, 96, 97, 98, and 100. Mo-98 is the most abundant and accounts for 24.14% of the natural element. Only Mo-100 is a radioactive. Including the natural isotopes, there are at least 39 isotopes, ranging from 81 to 119. The most stable synthetic isotope is Mo-93, which has a half-life of almost 5000 years. The radioisotope with the most practical applications is Mo-99, which finds use in medical imaging.

Abundance and Sources

Molybdenum does not occur free in nature. Its ores include molybdenite (MoS2), wulfenite (PbMoO4), and powellite (CaMoO4). Although not a common element in the Earth’s crust, it’s relatively more abundant in the universe. It is the 54th most abundant element in the Earth’s crust, 25th most abundant element in seawater, and 42nd most abundant element in the Universe. The largest producers of the metal are China, the United State, Chile, Peru, and Mexico.

Purification

The primary purification method starts with roasting the ore in air to obtain molybdenum(IV) oxide and sulfur dioxide. The next step is extracting the oxide using aqueous ammonia, yielding ammonium molybdate. Treating the resulting product with hydrogen sulfide removes copper, which is a common impurity. Upon heating, ammonium molybdate converts to solid ammonium dimolybdate and then molybdenum trioxide. Reducing the oxygen with hydrogen gives the purified metal.

Molybdenum Uses

Molybdenum is an element with many uses:

  1. Steel and Alloys:
    • Stainless Steel: Enhances corrosion resistance.
    • High-Speed Steel: Increases hardness and strength, used in cutting tools and drill bits.
    • High-Strength Steel: Improves strength and toughness.
    • Super Alloys: Essential for aerospace applications due to heat resistance.
  2. Catalysts:
    • Petroleum Industry: In desulfurization of crude oil.
    • Polymer Production: Catalyst in the production of plastics and synthetic rubbers.
    • Hydrocracking: Catalyzes the breakdown of heavy hydrocarbons into lighter compounds.
  3. Lubricants:
    • Molybdenum Disulfide (MoS2): A dry lubricant for high-temperature and high-pressure applications, effective where oils and greases cannot be used.
  4. Electronics and Electrical Applications:
    • Semiconductors: In thin-film transistors and photovoltaic cells.
    • Electrodes: In glass furnaces due to its high melting point and electrical conductivity.
  5. Chemical Industry:
    • Pigments and Dyes: In producing certain pigments and dyes for inks and textiles.
    • Corrosion Inhibitors: In certain types of industrial coolants and lubricants.
  6. Medical Applications:
    • Medical Imaging: Mo-99 decays to Tc-99m, for use in diagnostic imaging.
    • Dental Alloys: In dental prosthetics and orthopedics for its biocompatibility.
  7. Agriculture:
    • Fertilizers: Small amounts in certain fertilizers provide the essential nutrient for plant growth.
  8. Research and Development:
    • Scientific Instruments: In devices requiring heat resistance.
    • Experimental Physics: As a target material in particle accelerators.
  9. Nuclear Applications:
    • Nuclear Reactors: In nuclear fuel rods due to its ability to withstand high temperatures and as a neutron absorber.
  10. Automotive Industry:
    • Catalytic Converters: A catalyst in the reduction of nitrogen oxides in exhaust systems.
  11. Military Applications:
    • Armor Plating: In alloy form, for making armor plating more effective against impact.
  12. Glass and Ceramics Industry:
    • Glass Melting Electrodes: Due to its resistance to thermal shock and high melting point.
  13. Metal Working:
    • Metal Forming Equipment: In equipment subjected to high stress and temperatures, such as forging tools.
  14. Renewable Energy:
    • Photovoltaic Cells: Useful in some types of thin-film solar cells.

Oxidation States and Main States

Molybdenum exhibits various oxidation states: -4, -2, -1, 0 +1, +2, +3, +4, +5, and +6. The most common and stable states are +4 and +6. Molybdenum forms compounds with up to six covalent chemical bonds in Mo2.

Biological Role

Molybdenum is an essential trace element in almost all living organisms. It is a cofactor for enzymes involved in nitrogen fixation and the metabolism of sulfur and purines. It is an important trace nutrient for plants. In humans and other animals, it affects protein synthesis, growth, and metabolism. It also occurs in tooth enamel.

Insufficient molybdenum in the human diet affects the enzyme sulfite oxidase, leading to reactions to sulfites in food. Molybdenum deficiency also appears implicated in increased risk of esophageal cancer. On the other hand, excess exposure causes molybdenosis, leading to joint pain and increased uric acid levels. Other effects of excessive molybdenum include diarrhea, low birth weight, gout, and infertility. Too much molybdenum interferes with copper absorption, leading to copper deficiency. Inhalation of molybdenum dust causes respiratory issues.

Significant dietary sources of the element are beef liver, lamb, and pork. Other sources include eggs, wheat flour, cereal grain, cucumbers, green beans, and sunflower seeds.

Key Molybdenum Facts for Scientists

PropertyValue
NameMolybdenum
SymbolMo
Atomic Number42
Atomic Weight95.95
Group6
Period5
Blockd
Electron Configuration[Kr] 4d⁵ 5s¹
Electrons Per Shell2, 8, 18, 13, 1
State at Room TemperatureSolid
Melting Point2623 °C
Boiling Point4639 °C
Density10.223 g/cm³
Heat of Fusion37.48 kJ/mol
Heat of Vaporization598 kJ/mol
Molar Heat Capacity24.06 J/(mol·K)
Oxidation States-4, -2, -1, 0, +1, +2, +3, +4, +5, +6
Electronegativity (Pauling scale)2.16
Ionization Energies1st: 684.3 kJ/mol, 2nd: 1560 kJ/mol
Atomic Radius139 pm
Covalent Radius154 pm
Crystal StructureBody-centered cubic (bcc)
Thermal Conductivity138 W/(m·K)
Electrical Resistivity5.34 µΩ·m (at 20 °C)
Magnetic OrderingParamagnetic
Young’s Modulus329 GPa
Shear Modulus126 GPa
Bulk Modulus230 GPa
Mohs Hardness5.5

Interesting Molybdenum Facts

Here are some additional interesting molybdenum facts.

  • Radioactive Anomaly: Molybdenum is the only element among the first 92 that has a stable isotope (molybdenum-100) which undergoes double beta decay. This decay process is extremely rare and has a half-life over a thousand times the current age of the universe.
  • Early Life Connection: Molybdenum may have played a crucial role in the development of early life on Earth. It’s thought that the availability of molybdenum and its use in enzymes were critical for the development of nitrogen-fixing bacteria.
  • Colorful Compounds: Molybdenum compounds exhibit a wide range of vibrant colors. For example, molybdenum disulfide is a shiny dark gray or black, while molybdenum oxides are bright yellow or dark blue.
  • Meteorite Component: Molybdenum often occurs in meteorites in much higher concentrations than in the Earth’s crust.
  • Unique Alloys: The element is a key component in creating superalloys for jet engines and turbine blades due to their ability to withstand extreme heat without deformation.
  • Industrial Catalyst: Molybdenum is a catalyst in petroleum refining and in the production of certain polymers.
  • Historical Confusion: For a long time, molybdenum was used to make pencils, under the assumption it was graphite.
  • Environmental Indicator: The concentration of molybdenum in water sources is an indicator of industrial pollution from mining and industrial processes.

References

  • Abumrad, N. N. (1984). “Molybdenum—is it an essential trace metal?“. Bulletin of the New York Academy of Medicine. 60 (2): 163–71.
  • Brewer, G. J.; Dick, R. D.; Grover, D. K.; Leclaire, V.; Tseng, M.; Wicha, M.; Pienta, K.; Redman, B. G.; Jahan, T.; Sondak, V. K.; Strawderman, M.; LeCarpentier, G.; Merajver, S. D. (2000). “Treatment of metastatic cancer with tetrathiomolybdate, an anticopper, antiangiogenic agent: Phase I study”. Clinical Cancer Research. 6 (1): 1–10.
  • Considine, Glenn D., ed. (2005). “Molybdenum”. Van Nostrand’s Encyclopedia of Chemistry. New York: Wiley-Interscience. pp. 1038–1040. ISBN 978-0-471-61525-5.
  • Institute of Medicine (2000). “Molybdenum”. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: The National Academies Press. pp. 420–441. ISBN 978-0-309-07279-3. doi:10.17226/10026
  • Roos, Björn O.; Borin, Antonio C.; Laura Gagliardi (2007). “Reaching the Maximum Multiplicity of the Covalent Chemical Bond”. Angew. Chem. Int. Ed. 46 (9): 1469–1472. doi:10.1002/anie.200603600