- Molybdenum (Mo) is a transition metal with atomic number 42, located in Group 6 of the periodic table alongside chromium and tungsten.
- It is a hard, silvery-gray metal with high melting point and strength, notable for retaining its mechanical properties even at elevated temperatures.
- Molybdenum has six valence electrons—two in the 5s subshell and four in the 4d subshell—and it most commonly exhibits the +6 oxidation state, though +4 and +2 states also occur in certain compounds. Its atomic structure consists of forty-two protons, typically fifty-four neutrons, and forty-two electrons arranged in five shells.
- Naturally occurring molybdenum is composed of seven stable isotopes, with molybdenum-98 (⁹⁸Mo) being the most abundant (24.13%).
- Molybdenum is moderately abundant in the Earth’s crust at about 1.2 parts per million, comparable to tungsten but far less than iron. It is not found free in nature but occurs mainly in the mineral molybdenite (MoS₂), which is the primary commercial source, as well as in wulfenite (PbMoO₄) and powellite (CaMoO₄). Major producers include China, the United States, Chile, Peru, and Mexico. Molybdenum is extracted mainly through flotation concentration of molybdenite ore, followed by roasting to produce molybdenum trioxide (MoO₃), which can be further reduced to the pure metal.
- The element was first recognized in 1778 by Swedish chemist Carl Wilhelm Scheele, who demonstrated that molybdenite was neither graphite nor lead ore (galena) but a distinct mineral containing a new element. Metallic molybdenum was first isolated in 1781 by Swedish chemist Peter Jacob Hjelm by reducing molybdenum oxide with carbon. The name derives from the Greek molybdos, meaning “lead,” due to molybdenite’s resemblance to graphite and galena.
- Molybdenum’s primary industrial use is as an alloying element in steel and other metals to improve strength, hardness, toughness, and corrosion resistance, especially at high temperatures. Stainless steels, tool steels, and superalloys often contain molybdenum. It is also critical in petrochemical catalysts, where molybdenum sulfide (MoS₂) is used in hydrodesulfurization to remove sulfur from fuels. Molybdenum disulfide is also a solid lubricant with excellent performance in extreme conditions.
- In the electronics industry, molybdenum is used in thin films for transistors, electrodes for glass furnaces, and components in high-temperature vacuum systems. Its high melting point (2,623 °C) and low thermal expansion make it valuable in aerospace and defense applications.
- Chemically, molybdenum forms a variety of oxides, sulfides, and halides, and it can form coordination complexes in aqueous solutions. Molybdate ions (MoO₄²⁻) are an important chemical form, used in corrosion inhibitors, pigments, and fertilizers.
- Biologically, molybdenum is an essential trace element for many organisms, including humans. It functions as a cofactor in enzymes such as nitrogenase, xanthine oxidase, and sulfite oxidase, which are critical in nitrogen metabolism and detoxification processes. Dietary molybdenum is obtained from legumes, grains, and leafy vegetables. Deficiency is rare but can cause metabolic problems, while excessive exposure to molybdenum compounds may cause toxicity.
- From an environmental perspective, molybdenum is generally not considered a major pollutant, though mining operations must manage waste and prevent contamination of water sources. Its essential biological role means it is not inherently harmful at natural concentrations.
