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lanthanummore about 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 
  From  WordNet  r  1.6  [wn]: 
  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]: 
  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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