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lanthanum |
3 definitions found From Webster's Revised Unabridged Dictionary (1913) [web1913]: Lanthanum \Lan"tha*num\, n. [NL., fr Gr ? to lie hid, to be concealed.] (Chem.) A rare element of the group of the earth metals, allied to aluminium. It occurs in certain rare minerals, as cerite, gadolinite, orthite, etc., and was so named from the difficulty of separating it from cerium, didymium, and other rare elements with which it is usually associated. Atomic weight 138.5. Symbol La [Formerly written also {lanthanium}.] From WordNet r 1.6 [wn]: lanthanum n : a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth [syn: {La}, {atomic number 57}] From Elements database 20001107 [elements]: lanthanum Symbol: La Atomic number: 57 Atomic weight: 138.9055 (From the Greek word lanthanein to line hidden) Silvery metallic element belonging to group 3 of the periodic table and oft considered to be one of the lanthanoids. Found in some rare-earth minerals. Twenty-five natural isotopes exist. La-139 which is stable, and La-138 which has a half-life of 10^10 to 10^15 years. The other twenty-three isotopes are radioactive. It resembles the lanthanoids chemically. Lanthanum has a low to moderate level of toxicity, and should be handled with care Discovered in 1839 by C.G. Mosander.
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