'Lanthanum' definitions:
Definition of 'lanthanum'
From: WordNet
noun
A white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth [syn: lanthanum, La, atomic number 57]
Definition of 'Lanthanum'
From: GCIDE
- 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, gadolinite, orthite, etc., and was so named from the difficulty of separating it from cerium, didymium, and other rare earth elements with which it is usually associated. Atomic weight 138.9. Symbol La. [Formerly written also lanthanium.] [1913 Webster]
Definition of 'Lanthanum'
From: Elements
- Symbol: La
- Atomic number: 57
- Atomic weight: 138.9055
- (From the Greek word lanthanein, to lie 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.