lanthanum


lanthanum
/lan"theuh neuhm/, n. Chem.
a rare-earth, trivalent, metallic element, allied to aluminum, found in certain minerals, as monazite. Symbol: La; at. wt.: 138.91; at. no.: 57; sp. gr.: 6.15 at 20°C.
[ < NL (1841), equiv. to lanthan- ( < Gk lanthánein to escape notice; referring to its position on the periodic table) + -um, var. of -ium -IUM]

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 (La), chemical element, rare-earth metal of transition Group IIIb of the periodic table, prototype of the lanthanoid series of elements. Lanthanum is a ductile and malleable, silvery-white metal, soft enough to be cut with a knife. The element was discovered as the oxide (lanthana) in 1839 by Carl Gustaf Mosander (Mosander, Carl Gustaf), who distinguished it from cerium oxide (ceria). Its name is derived from the Greek lanthanein, meaning “to be concealed,” indicating that it is difficult to isolate.

      Lanthanum occurs in the rare-earth minerals monazite and bastnaesite. It is concentrated commercially by crystallization of ammonium lanthanum nitrate. Ion-exchange and solvent extraction methods are used when high purity is desired. The metal itself is prepared by electrolysis of fused anhydrous halides or by reduction of its halides by alkali or alkaline-earth metals (e.g., reduction of the fluoride with calcium). misch metal—used as cigarette-lighter flints, as a getter that removes traces of oxygen in electron tubes, and in metallurgy—is one-fourth lanthanum.

      Lanthanum exhibits three allotropic (structural) forms. Two isotopes occur in nature: stable lanthanum-139 (99.911 percent) and very long-lived radioactive lanthanum-138 (0.089 percent). The isotope lanthanum-140 has been detected as a fission product in snow after nuclear-test explosions.

      Lanthanum is the second most reactive of the rare-earth metals (europium is first); it rapidly tarnishes in dry air, ignites in air at 440° C (824° F), and reacts vigorously with hot water. In its compounds its only oxidation state is +3. The ionic radius is the largest of the rare-earth M3+ ions, and as a consequence the white oxide La2O3 is the most alkaline rare-earth oxide.

      Highly purified lanthanum oxide is an ingredient in the manufacture of low-dispersion, high-refraction glasses for lens components. The technical grade fluoride is used as core material for arc-light carbons.

atomic number
57
atomic weight
138.91
melting point
920° C (1,688° F)
boiling point
3,454° C (6,249° F)
specific gravity
6.166 (25° C)
oxidation state
+3
electronic config.
[Xe]5d16s2

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Universalium. 2010.

Look at other dictionaries:

  • Lanthanum — (pronEng|ˈlænθənəm) is a chemical element with the symbol La and atomic number 57. Characteristics Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a lanthanoid. Found in some rare earth minerals …   Wikipedia

  • 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… …   Elements of periodic system

  • lanthanum — [lan′thənəm] n. [ModL: so named (1839) by G. Mosander (see ERBIUM) < lanthana, lanthanum oxide, lit., the hidden one < Gr lanthanein, to be hidden (see LATENT): it had previously been undetected in the mineral cerite] a soft, malleable,… …   English World dictionary

  • Lanthanum — Lan tha*num (l[a^]n th[.a]*n[u^]m), n. [NL., fr. Gr. lanqa nein to lie hid, to be concealed.] (Chem.) A rare element of the rare earth group of the metals, of atomic number 57, allied to aluminum. It occurs in certain rare minerals, as cerite,… …   The Collaborative International Dictionary of English

  • lanthanum — salts are used as a negative stain in electron microscopy, and as calcium channel blockers …   Dictionary of molecular biology

  • lanthanum — metallic rare earth element, 1841, coined in Modern Latin by Swedish chemist and mineralogist Carl Gustav Mosander (1797 1858), who discovered it in 1839, from Gk. lanthanein to lie hidden, escape notice, from PIE root *ladh to be hidden (see… …   Etymology dictionary

  • lanthanum — lantanas statusas T sritis chemija apibrėžtis Cheminis elementas. simbolis( iai) La atitikmenys: lot. lanthanum angl. lanthanum rus. лантан …   Chemijos terminų aiškinamasis žodynas

  • lanthanum — noun [lɑ˧nˈðaː˨nɔ˧m] a) A metallic chemical element (symbol La) with an atomic number of 57. b) lanthanum See Also: lanthana, lanthanate, lanthanide, lanthanite, lanthanoid, lanthanon …   Wiktionary

  • lanthanum — lantanas statusas T sritis fizika atitikmenys: angl. lanthanum vok. Lanthan, n rus. лантан, m pranc. lanthane, m …   Fizikos terminų žodynas

  • lanthanum — noun Etymology: New Latin, from Greek lanthanein to escape notice more at latent Date: 1841 a white soft malleable metallic element that occurs in rare earth minerals see element table …   New Collegiate Dictionary


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