praseodymium

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praseodymium

(prā'zēōdĭm`ēəm, –sēō–) [Gr., =green twin], metallic chemical element; symbol Pr; at. no. 59; at. wt. 140.90765; m.p. 931°C;; b.p. 3,512°C;; sp. gr. about 6.8; valence +3 or +4. Praseodymium is a soft, malleable, ductile, silver-yellow metal. It exhibits allotropyallotropy
[Gr.,=other form]. A chemical element is said to exhibit allotropy when it occurs in two or more forms in the same physical state; the forms are called allotropes.
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; the α-form (hexagonal crystalline structure) has the density given above, but the β-form (above 800°C;, body-centered cubic crystalline structure) is less dense. Praseodymium is a rare-earth metalrare-earth metals,
in chemistry, group of metals including those of the lanthanide series and actinide series and usually yttrium, sometimes scandium and thorium, and rarely zirconium. Promethium, which is not found in nature, is not usually considered a rare-earth metal.
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 of the lanthanide serieslanthanide series,
a series of metallic elements, included in the rare-earth metals, in Group 3 of the periodic table. Members of the series are often called lanthanides, although lanthanum (atomic number 57) is not always considered a member of the series.
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 in Group 3 of the periodic tableperiodic 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 table entitled
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. When exposed to air it forms a green oxide that does not protect it from further oxidation. Although the pure metal may be prepared by reduction of the chloride, it has few commercial uses. A major use of the metal is in a pyrophoric alloy used in cigarette lighter flints, but it need not be purified for this application. Praseodymium compounds have many uses. The oxide is used in carbon electrodes for arc lighting. The salts are used to color enamels and glass. Didymium glass used in glassblower's goggles contains praseodymium; this glass absorbs the yellow sodium glare of light from the torch flame. The major commercial source of praseodymium is the rare-earth minerals monazitemonazite
, yellow to reddish-brown natural phosphate of the rare earths, mainly the cerium and lanthanum metals, usually with some thorium. Yttrium, calcium, iron, and silica are frequently present.
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 and bastnasite. Praseodymium was discovered in 1885 by C. A. Von WelsbachWelsbach, Carl Auer, Baron von
, 1858–1929, Austrian chemist. He discovered the rare earth elements neodymium and praseodymium (1885) and lutetium (c.1908, independently of the French chemist Georges Urbain). He is known also for the invention of the Welsbach mantle.
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, who separated Mosander's "didymium" into two components, the earths neodymia and praseodymia.

praseodymium

[‚prā·zē·ō′dim·ē·əm]
(chemistry)
A chemical element, symbol Pr, atomic number 59, atomic weight 140.9077; a metallic element of the rare-earth group.

praseodymium

a malleable ductile silvery-white element of the lanthanide series of metals. It occurs principally in monazite and bastnaesite and is used with other rare earths in carbon-arc lights and as a pigment in glass. Symbol: Pr; atomic no.: 59; atomic wt.: 140.90765; valency: 3; relative density: 6.773; melting pt.: 931°C; boiling pt.: 3520°C