Atomic number 42
Atomic mass 95.94 g.mol -1
Electronegativity according to Pauling 1.8
Density 10.2 g.cm-3 at 20°C
Melting point 2610 °C
Boiling point 4825 °C
Vanderwaals radius 0.139 nm
Ionic radius 0.068 nm (+4) ; 0.06 nm (+6)
Electronic shell [ Kr ] 4d5 5s1
Energy of first ionisation 651 kJ.mol -1
Standard potential - 0.2 V
The metal is silvery white, very hard transition metal, but is softer and more ductile than tungsten. Scheele discovered it in 1778. It was often confused with graphite and lead ore. It has a high elastic modulus, and only tungsten and tantalum, of the more readily available metals, have higher melting points. Molybdenum has one of the highest melting points of all pure elements. Molybdenum is attacked slowly by acids.
Molybdenite is the chief mineral ore, with wulfenite being less important. Some molybdenite is obtained as a by-product of tungsten and copper production. The main mining areas are the USA, Chile, Canada and Russia, with world production being around 90.000 tonnes per year, and reserves amounting to 12 million tonnes of which 5 million tonnes are in the USA.
Molybdenum is a valuable alloying agent, as it contributes to the hardenability and toughness of quenched and tempered steels. It also improves the strength of steel at high temperatures. Molybdenum is used in alloys, electrodes and catalysts. The Second World War German artillery piece called "Big Bertha" contains molybdenum as an essential component of its steel.
It is used in certain nickel-based alloys, such as the "Hastelloys(R)" which are heat-resistant and corrosion-resistant to chemical solutions. Molybdenum oxidizes at elevated temperatures. The metal has found recent application as electrodes for electrically heated glass furnaces and foreheaths. The metal is also used in nuclear energy applications and for missile and aircraft parts. Molybdenum is valuable as a catalyst in the refining of petroleum. It has found applications as a filament material in electronic and electrical applications. Molybdenum is an essential trace element in plant nutrition. Some lands are barren for lack of this element in the soil. Molybdenum sulfide is useful as a lubricant, especially at high temperatures where oils would decompose. Almost all ultra-high strength steels with minimum yield points up to 300,000 psi(lb/in.2) contain molybdenum in amounts from 0.25 to 8%.
Molybdenum powders are used in circuit inks for circuit boards, and in microwaves devices and heat sinks for solid-state devices.