Molybdenum, element number 42 of the periodic table, lies in the table's second transition series, in Group 6A between chromium and tungsten.
It has one of the highest melting temperatures of all the elements, yet unlike most other high-melting point metals, its density is only 25% greater than iron's. Its coefficient of thermal expansion is the lowest of the engineering materials, while its thermal conductivity exceeds all but a handful of elements.
When added to steel and cast irons, molybdenum enhances strength, hardenability, weldability, toughness, elevated temperature strength, and corrosion resistance. In nickel-base alloys, it improves resistance to both corrosion and high-temperature creep deformation.
Molybdenum-based alloys have a unique combination of properties, including high strength at elevated temperatures, high thermal and electrical conductivity, and low thermal expansion. Molybdenum metal and its alloys are the first choice in many demanding specialized applications.
Chemically, the outstanding feature of molybdenum is its extraordinary versatility:
- Oxidation states from –II to VI
- Coordination numbers from 4 to 8
- Varied stereochemistry
- The ability to form compounds with inorganic and organic ligands, with particular preference for oxygen, sulfur, fluorine and chlorine donor atoms
- Formation of bi- and poly-nuclear compounds containing bridging oxide or chloride ligands and/or molybdenum-molybdenum bonds.