| 单词 | lanthanum | |||
| 释义 | lanthanumlan·tha·numL0044500 (lăn′thə-nəm)lanthanum(ˈlænθənəm)lan•tha•num(ˈlæn θə nəm)n. lan·tha·num(lăn′thə-nəm)
lanthanumlanthanum(lăn`thənəm) [Gr.,=to lie hidden], metallic chemical element; symbol La; at. no. 57; at. wt. 138.90547; m.p. about 920°C;; b.p. about 3,460°C;; sp. gr. 6.19 at 25°C;; valence +3. Lanthanum is a soft, malleable, ductile, silver-white metal; at room temperature it has a hexagonal close-packed crystalline structure that is unstable at higher temperatures (see 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. ..... Click the link for more information. ). Lanthanum is usually considered the first member 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. ..... Click the link for more information. , a group of elements with similar physical and chemical properties. It is one of the rare-earth metalsrare-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. ..... Click the link for more information. of 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 ..... Click the link for more information. . Lanthanum is a chemically active element. It oxidizes rapidly in air and reacts with water to form the hydroxide. It reacts readily with acids, with elemental boron, carbon, nitrogen, phosphorus, selenium, silicon, or sulfur, and with the halogens. The oxide and the boride are used in electronic vacuum tubes; the oxide is added to optical glass to increase its alkali resistance and refractive index. Its aluminate is a perovskite ceramic used as a superconductor substrate. Although lanthanum is not found uncombined in nature, it occurs in 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. ..... Click the link for more information. and bastnasite. Lanthanum may be prepared by reduction of lanthanum fluoride with calcium metal. Lanthanum is used in rechargeable nickel-metal hydride batteries. It may be used in making ductile cast ironiron, metallic chemical element; symbol Fe [Lat. ferrum]; at. no. 26; at. wt. 55.845; m.p. about 1,535°C;; b.p. about 2,750°C;; sp. gr. 7.87 at 20°C;; valence +2, +3, +4, or +6. Iron is biologically significant. ..... Click the link for more information. ; alloyed with other metals, it is used in cigarette lighter flints. Natural lanthanum is a mixture of two stable isotopes. One radioactive byproduct of the fission of plutonium, thorium, or uranium is a mixture of radioactive isotopes of lanthanum; 17 radioactive isotopes are known. Lanthanum was discovered in the form lanthanium oxide, called lanthana, in 1839 by C. G. Mosander. lanthanum[′lan·thə·nəm]lanthanumlanthanumlanthanum(La) [lan´thah-num]lan·tha·num (La),(lan'thă-nŭm),lan·tha·num(lan'thă-nŭm)lanthanum
Synonyms for lanthanum
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lanthanum - a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth