Introduction
Molybdenum is a transition metal present in group number VI B of the periodic table. Its atomic number is 42 whereas its atomic mass is 95.95. It has 42 electrons. Molybdenum has 42 protons and 56 neutrons in its nucleus. It is represented by the symbol “Mo”.
Naming and History
The word Molybdenum is derived from the Greek word “Molybdos” which means lead.
Molybdenite, likewise called molybdena was commonly confused for graphite and it was believed to include lead.
- Carl W. Scheele
In 1778 Swedish scientist Carl W. Scheele verified that molybdenite was not graphite neither did it have lead.
Scheele concluded that the mineral included a new element, but he did not isolate it, as he did not have an appropriate furnace to reduce the white solid to the metal.
- Peter J. Hjelm
In 1781, Scheele’s good friend and compatriot, Peter J. Hjelm separated the metal by reducing the white solid with carbon. He ground the two substances together making use of linseed oil to create a paste.
The paste ensured intimate contact between the carbon and molybdenite. Hjelm heated the combination highly in a shut crucible to produce the new metallic element. Hjelm called his new metal molybdenum.
Occurrence of Molybdenum
Molybdenum does not occur freely in nature. It is present in ores and minerals. Today, the majority of molybdenum is acquired from molybdenite, wulfenite (PbMoO4), and powellite (CaMoO4).
These ores typically occur along with ores of tin and tungsten. Molybdenum is also obtained as a by-product of the mining of tungsten and copper. The major mining areas are Chile, Canada, and Russia.
Properties of Molybdenum
Molybdenum is silvery-white, hard transition metal, but is softer than tungsten. It has a high elastic modulus. It does not react with oxygen or water at room temperature and also it also withstands corrosion at standard temperature.
Of the readily available metals, only tungsten and tantalum have higher melting points. The melting point of molybdenum is 2623 ° C and its boiling point is 4639 ° C. It has a density of 10.2 grams per cubic centimeter and exists as solid at room temperature.
Molybdenum in Biological System
Molybdenum is a toxic element but trace amounts of it are required for living organisms. It is necessary for the proper functioning of enzymes. Almost 50 enzymes in plants and animals need molybdenum.
The enzyme nitrogenase contains molybdenum which is present in nitrogen-fixing bacteria. These are also present in leguminous plants.
Uses of Molybdenum
- It is mainly alloyed with steel to increase its hardness, toughness, strength, conductivity, and resistivity to corrosion.
- It is used in electrodes and as a catalyst in the refining of petroleum.
- Due to its resistivity and strength, it is used in power plants, nuclear reactors, and aircraft engines.
- Molybdenum sulphide is used as high-temperature lubricant.
- It is used in making filaments of light bulbs.
- Molybdenum powders are greatly produced and sold. These are used in circuits, microwave parts, and heat sinks for solids.
Isotopes of Molybdenum
Molybdenum has 24 isotopes whose half-lives are known with mass numbers from 86 to 110. Naturally occurring molybdenum is a mix of seven isotopes. The most abundant is 98- Mo at 24.1%.