/ak tin"ee euhm/, n. Chem.
a radioactive silver-white metallic element that glows blue in the dark, resembling the rare earths in chemical behavior and valence. Symbol: Ac; at. no.: 89; at. wt.: 227.
[1900-05; ACTIN- + -IUM]

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 (Ac), radioactive chemical element, in Group IIIb of the periodic table, atomic number 89. Actinium was discovered (1899) by André-Louis Debierne in pitchblende residues left after Pierre and Marie Curie had extracted radium and was also discovered (1902) independently by Friedrich Otto Giesel. A ton of pitchblende ore contains about 0.15 mg of actinium. The rare, silvery-white metal is highly radioactive, glowing blue in the dark.

      The most common isotope of actinium is actinium-227; the others, natural and artificial, are too short-lived to accumulate in macroscopic quantity. Actinium-227, which is one of the decay products of uranium-235, has a 21.6-year half-life and in turn decays almost entirely to thorium-227, but about 1 percent decays to francium-223. This whole disintegration chain with its branches is called the actinium (actinium series) decay series.

      Actinium, the ions of which in solution are colourless, exhibits an oxidation state of +3, closely resembling the rare-earth lanthanoid elements in its chemical properties, and is the prototype of a second rare-earth-like series, the actinoid elements.

atomic number
stablest isotope
oxidation state
electronic config.

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Universalium. 2010.

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  • ACTINIUM — L’existence dans la pechblende de l’actinium, élément radioactif de numéro atomique 89, fut établie en 1899 par André Louis Debierne, collaborateur de Pierre et Marie Curie qui venaient, un an auparavant, de découvrir, dans ce minerai d’uranium,… …   Encyclopédie Universelle

  • Actinium — (pronEng|ækˈtɪniəm) is a radioactive chemical element with the symbol Ac and atomic number 89, which was discovered in 1899, the earliest discovered of the radioactive elements.CharacteristicsActinium is a silvery, radioactive, metallic element.… …   Wikipedia

  • Actinium — Radium ← Actinium → Thorium La …   Wikipédia en Français

  • Actinium — Ac*tin i*um, n. [Gr. ?, ?, ray.] (Chem.) A supposed metal, said by Phipson to be contained in commercial zinc; so called because certain of its compounds are darkened by exposure to light. [1913 Webster] …   The Collaborative International Dictionary of English

  • actinium — ACTÍNIUM s.n. v. actiniu. Trimis de LauraGellner, 13.09.2007. Sursa: DN …   Dicționar Român

  • actinium — Symbol: Ac Atomic number: 89 Atomic weight: (227) Silvery radioactive metallic element, belongs to group 3 of the periodic table. The most stable isotope, Ac 227, has a half life of 217 years. Ac 228 (half life of 6.13 hours) also occurs in… …   Elements of periodic system

  • actinium — (n.) radioactive element discovered in 1899, from Gk. actin , comb. form of aktis (gen. aktinos) ray, radiance (see ACTINO (Cf. actino )) + chemical suffix ium …   Etymology dictionary

  • actinium — [ak tin′ē əm] n. [ModL < ACTINO + IUM] a white, radioactive, metallic chemical element, the first member of the actinide series, found in pitchblende and other minerals or formed in reactors by the neutron irradiation of radium: symbol, Ac; at …   English World dictionary

  • actinium K — actinium K, the name originally given to element number 87 by its discoverer, who changed it to francium in 1947 …   Useful english dictionary

  • Actinium — Eigenschaften …   Deutsch Wikipedia

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