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Columbia Encyclopedia entry: technetium

Technetiumtĕknē'shēəm [Gr. technetos=artificial], artificially produced radioactive chemical element; symbol Tc; at. no. 43; mass no. of most stable isotope 98; m.p. 2,200°C; b.p. 4,877°C; sp. gr. 11.5 (calculated); valence +4, +6, or +7. Technetium is a radioactive silver-gray metal. In some of its chemical properties it resembles rhenium, the element below it in Group 7 of the periodic table. It tarnishes slowly when exposed to moist air. Although it is not attacked by hydrochloric acid, it dissolves in concentrated sulfuric or nitric acid and in aqua regia. The pure metal may be prepared by chemical reduction of certain of its compounds with hydrogen gas. Potassium technetate, KTcO4, has found some use in alloys with iron and steel; the addition of a small amount renders the alloy highly resistant to corrosion. This use is limited by the radioactivity of the element. The most stable isotope, technetium-98, has a half-life of 4.2 million years; most of the other 30 known isotopes are much less stable. Technetium-95m is a gamma-ray emitter with a half-life of 61 days that is used in radioactive tracer studies. The most useful isotope of technetium, however, is technetium-99m, which is used in many medical radioactive isotope tests because of its short half-life (6.01 hours), the energy of the gamma radiation it emits, and its ability to bind chemically to many biologically active molecules. Technetium was once very rare and expensive but is now obtained in quantity from nuclear reactor fission products. Although the spectra of some stars show that they contain technetium, the naturally occurring element has not been found on earth. It is called technetium because it was the first element to be prepared synthetically. Its existence was predicted from the periodic table. Discovery of the element in nature was erroneously claimed in 1925 by the German chemists I. W. and W. K. Noddack, who called it masurium. The element was discovered in 1937 by C. Perrier and E. G. Segrè of Italy in a sample of molybdenum that was bombarded with deuterons in a cyclotron at the Univ. of California at Berkeley and sent to them by E. O. Lawrence.

Wikipedia search results for: Technetium

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Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes. Nearly all of technetium is produced synthetically and only minute amounts are found in nature. Naturally occurring technetium occurs as a spontaneous fission product in uranium ore or by neutron capture in molybdenum ores. The chemical properties of this silvery gray, crystalline transition metal are intermediate between rhenium and manganese. Many of technetium's properties were predicted by Dmitri Mendeleev before the element was discovered. Mendeleev noted a gap in his periodic table and gave the undiscovered...more »

Columbia Encyclopedia search results: technetium

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Periodic Table of the Elements: Technetium
Periodic Table of the Elements: TechnetiumAtomic Number:43Atomic Symbol:TcTechnetiumAtomic Weight:(98)ElectronConfiguration:2 · 8 · 1813 · 2
Tc
Tc, symbol for the element technetium.
synthetic elements
Synthetic elements, in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetium (at. no. 43), which was the first...
rhenium
Rhenium, metallic chemical element; symbol Re; at. no. 75; at. wt. 186.207; m.p. about 3,180°C; b.p. about 5,625°C; sp. gr. 21.02 at 20°C; valence -1, +2, +3, +4, +5, +6, or +7. Rhenium is a v...
Elements (table)
ElementsElementSymbolAtomic NumberAtomic Weight1Melting Point(Degrees Celsius)Boiling Point(Degrees Celsius)1 Parentheses indicate most stable isotope.actiniumAc89227.02781050.3200....
element
Element, in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound can be decomposed into its constituent elements by means ...

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