actinium definition of actinium in the Free Online Encyclopedia.

actinium (ăktĭn`ēəm) [Gr.,=like a ray], radioactive chemical element; symbol Ac; at. no. 89; at. wt. 227.0278; m.p. about 1,050°C;; b.p. 3,200°C;±300°C;; sp. gr. 10.07; valence +3. Actinium is a silver-white metal with a cubic crystalline structure. It is found with uranium minerals in pitchblende pitchblende (pĭch`blĕnd'), dark, lustrous, heavy mineral, a source of radium and uranium.
..... Click the link for more information. . The pure metal can be prepared by reducing its fluoride with lithium vapor at about 1,200°C;. Actinium-227, the most stable isotope, has a half-life half-life, measure of the average lifetime of a radioactive substance (see radioactivity ) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay.
..... Click the link for more information. of 21.6 years. The other seven isotopes of actinium have very short half-lives ranging from 10 days to less than 1 min. Actinium is in Group 3 of the periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley . In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the
..... Click the link for more information. . Its chemical properties are similar to those of lanthanum lanthanum (lăn`thənəm) [Gr.,=to lie hidden], metallic chemical element; symbol La; at. no. 57; at. wt. 138.9055; m.p.
..... Click the link for more information. and of members of the actinide series actinide series, a series of radioactive metallic elements in Group 3 of the periodic table . Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series.
..... Click the link for more information. , of which it is usually considered the first member. It reacts with water to form an insoluble hydroxide; with halides to form a trifluoride, trichloride, bromide, or iodide; with oxalic acid to form the oxalate; with oxygen or sulfur to form the sesquioxide or sesquisulfide. Actinium was first recognized in 1899 by André Debierne in uranium residues from pitchblende after the radium was extracted by Pierre and Marie Curie Pierre Curie, 1859–1906, scientist, and his wife,

Marie Sklodowska Curie, 1867–1934, chemist and physicist, b. Warsaw, are known for their work on radioactivity and on radium.
..... Click the link for more information. . It was later found to be identical with an element discovered in 1902 by Fritz Giesel and which he called emanium.

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actinium