[lan-thuh-nuh
m] 
| a rare-earth, trivalent, metallic element, allied to aluminum, found in certain minerals, as monazite. Symbol: La; atomic weight: 138.91; atomic number: 57; specific gravity: 6.15 at 20°C. |
| lan·tha·num (lān'thə-nəm) n. Symbol La A soft, silvery-white, malleable, ductile, metallic rare-earth element, obtained chiefly from monazite and bastnaesite and used in glass manufacture and with other rare earths in carbon lights for movie and television studio lighting. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,469°C; specific gravity 5.98 to 6.186; valence 3. See Table at element. [New Latin, from Greek lanthanein, to escape notice (from the finding of the element hidden in oxide of cerium).] |
lanthanum lan·tha·num (lān'thə-nəm)
n.
Symbol La
A soft malleable metallic rare-earth element used in glass manufacture. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,455°C; specific gravity 6.145 (at 25°C); valence 3.
| lanthanum (lān'thə-nəm) Pronunciation Key
Symbol La A soft, malleable, silvery-white metallic element of the lanthanide series. It is used to make glass for lenses and lights for movie and television studios. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,469°C; specific gravity 5.98 to 6.186; valence 3. See Periodic Table. |
lanthanum
((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, 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
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