technetium

/tek nee"shee euhm, -sheuhm/, n.

Chem. an element of the manganese family, not found in nature, but obtained in the fission of uranium or by the bombardment of molybdenum. Symbol: Tc; at. wt.: 99; at. no.: 43; sp. gr.: 11.5.

[1945-50; < Gk technet(ós) artificial (lit., made, verbid of technâsthai; see TECHNO-) + -IUM]

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Metallic chemical element, one of the transition elements, chemical symbol Tc, atomic number 43.

All its isotopes are radioactive (see radioactivity); some occur in trace amounts in nature as nuclear fission products of uranium. Its isotope technetium-97 was the first element artificially produced (1937; see cyclotron). Technetium-99, a fission product of nuclear reactors that emits gamma rays, is the most-used tracer isotope in nuclear medicine. Technetium resembles platinum in appearance and manganese and rhenium in chemical behaviour. It is also used as a metallurgical tracer and in corrosion-resistant products.

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▪ chemical element

 chemical element, synthetic radioactive metal of Group 7 (VIIb) of the periodic table, the first element to be artificially produced. The isotope technetium-97 (2,600,000-year half-life) was discovered (1937) by the Italian mineralogist Carlo Perrier and the Italian-born American physicist Emilio Segrè (Segrè, Emilio) in a sample of molybdenum that had been bombarded by deuterons in the Berkeley (California) cyclotron. This isotope is the longest-lived member of a set from technetium-92 to technetium-107 that has since been produced. The most important isotope, because it is the only one available on a large scale, is technetium-99 (212,000-year half-life); it is produced in kilogram quantities as a fission product in nuclear reactors. Technetium metal looks like platinum but is usually obtained as a gray powder. It crystallizes in the hexagonal close-packed structure and is a superconductor below 11.2 K. Except for technetium-99, technetium-97, and technetium-98 (1,500,000-year half-life), technetium isotopes are short-lived. Technetium has essentially no uses.

      Technetium occurs in the Earth's crust as minute traces from the spontaneous fission of uranium; the relatively short half-lives preclude the existence of any primordial technetium on Earth. The American astronomer Paul W. Merrill's discovery in 1952 that technetium-99 is present in S-type stars was a valuable piece of evidence concerning stellar evolution and nucleosynthesis. Technetium, chemically similar to rhenium (atomic number 75), exists in oxidation states of +7, +6, and +4 in compounds such as potassium pertechnetate, KTcO₄, technetium chloride, TcCl₆, and technetium sulfide, TcS₂, respectively. Compounds are known in all formal oxidation states from −1 to +7.

atomic number

43

commonest isotope

(99)

melting point

2,172° C (3,942° F)

boiling point

4,877° C (8,811° F)

specific gravity

11.5 (20° C)

oxidation states

+4, +6, +7

electronic config.

[Kr]4d⁶5s¹

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