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Element Fact
Iridium is the most corrosion-resistant metal known. Together with platinum, it is used to make the international prototype of the kilogram, which is the standard definition for the unit of mass.

Tungsten, W

tungsten sample

Atomic number: 74
Atomic mass: 183.84(1)
Natural abundance: 1.2 ppm
180W (179.946706) - 0.13%
182W (181.948206) - 26.3%
183W (182.950224) - 14.3%
184W (183.950933) - 30.67%
186W (185.954362) - 28.6%

History and Production

From Swedish word tung sten, meaning heavy stone. P. Woulfe examined a mineral sample of wolframite ((Fe,Mn)WO4) in 1779 and suspected a new element may be contained in the mineral. In 1781, C.W. Scheele and T. Bergmann isolated a new acid from a mineral called 'tungsten' (CaWO4) but now it is known as scheelite. In 1783, J.J. d'Elhuyar and F. d'Elhuyar, two Spanish brothers, showed that the acid was also a constituent of the mineral wolframite and subsequently reduced it to metal by charcoal. Nowadays, the commercial sources are still obtained from these minerals. Depends on the ores being used, both are converted to the oxide (WO3) which is reduced to metal by heating with hydrogen at 850C. It is used mainly as filaments in electric light bulbs, electron and television tubes. It is also used as X-ray targets and heating elements in electric furnaces. It has also an important use as glass-metal seals. The carbide (WC), being one of the hardest substance is important in making tool-tips such as drill bits. Tungsten disulfide is used as a high-temperature lubricant.

Physical Data

The metal is lustrous, silvery gray in color. It has the highest melting point of all metals. It has a small thermal expansion coefficient which is comparable to borosilicate glass. The pure metal can be easily worked on but the impure metal is brittle. It consists of 1.2 ppm of the earth's crust in minerals such as scheelite, wolframite, ferberite (FeWO4) and huebnerite (MnWO4).

Interatomic distance: 274 pm
Melting point: 3422C
Boiling point: 5555C
Thermal conductivity/Wm-1K-1: 174 (27C)
Density/kgm-3: 19300 (20C), 17700 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 849.4 kJ/mol
Gibbs free energy of formation: 807.1 kJ/mol
Entropy: 174.0 J/mol K
Heat capacity: 21.3 J/mol K

Electronic data

Electronic configuration: [Xe] 4f14 5d4 6s2
Term symbol: 5D0
Electron affinity: 78.6356 kJ/mol   Electronegativity (Pauline): 1.7
Ionization energy (first, second, third): 758.761, -, - kJ/mol

Chemical properties

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