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Element Fact
Selenium is an essential trace element in the diets that acts as antioxidants.

Technetium, Tc

technetium sample

Atomic number: 43
Atomic mass: [98] (has no stable nuclide)
Natural abundance: - ppm
98Tc (97.907216) - *
99Tc (98.906255) - *

History and Production

The name was derived from the Greek technetos, meaning artificial. The name was quite rightly given because it is the first element to be produced artificially. The element 'masurium' was erroneously reported as having been discovered in 1925. However, the element with the atomic number 43 was actually discovered by C. Perrier and E. Segr in 1937 when a smaple of molybdenum was bombarded with deuterons in the cyclotron of E.O. Lawrence in California. The isotopes 95Tc and 97Tc, as a result, were formed. The metal can be produced in the fission products of the nuclear reactions. The use of the metal is not significant due to its lack of availability in nature. It is found to be good corrosion inhibitor for steel. However, the use is only confined to close systems since technetium is radioactive. Its main use is in diagnostic nuclear medicine, in the form of metastable gamma-emitting isotope 99mTc.

Physical Data

The metal is silvery-grey in appearance that tarnishes slowly in air. In nature, the metal may exist in traces as 99Tc with a half-life of 2.14 x 105 years, which is formed as a result of spontaneous fission of uranium.

Interatomic distance: 270.4 pm
Melting point: 2157C
Boiling point: 4265C
Thermal conductivity/Wm-1K-1: 50.6 (27C)
Density/kgm-3: 11500 (20C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 678.0 kJ/mol
Gibbs free energy of formation: - kJ/mol
Entropy: 181.1 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Kr] 4d5 5s2
Term symbol: 6S5/2
Electron affinity: 53.0670 kJ/mol   Electronegativity (Pauline): 2.10
Ionization energy (first, second, third): 702.414, 1472.37, 2850.18 kJ/mol

Chemical properties

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