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H' at. wt. (natural) 1.007967
   at. wt. (H') 1.007822
   at. no. 1
   m.p. - 259.140C
   b.p. - 252.870C 
   density 0.08988 gm./l
   density (liquid) 70.8 gm/i. (-2530C)
   density (solid) 7016 gm/i. (-2620C)
   valence 1.

**Electronic configuration**
K	L	M	N	O	P	Q
1	2	3	4	5	6	7
s	s p	s p d	s p d f	s p d f	s p d f	s p d f
1

LUTETIUM (Lutetia, ancient name for Paris-some- times called cassiopelum by the Germans). Lu; at. wt. 174.97; at. no.71; m.p. 1656j50C; b.p. 33150C; sp. gr. 9.835 (250C); valence 3. In 1907 Urbain described a process by which Marignac's ytterbium (1879) could be separated into the two elements, ytterbium (neoytterbium) and lutetium. These elements were identical with "aldebar- anium" and "cassiopeium" independently discovered by von Welsbach about the same time. Charles James of the University of New Hampshire also independently prepared the very pure oxide, lutecia; at this time. The spelling of the element was changed from lutecium to lutetium in 1949. Lutetium occurs in very small amounts in nearly all minerals containing yttrium, and is present in monazite to the extent of about 0.003 %, which is a commercial source. The pure metal has been isolated only in recent years and is one of the most difficult to prepare. It can be prepared by the reduction of anhydrous LuCI3 or LuF3 by an alkali or alkaline earth metal. The metal is silvery white and relatively stable in air. While new techniques, including ion exchange reactions, have been developed to separate the various rare earth elements, lutetium is still the most costly of all naturally occurring rare earths. It is slightly more abundant than thulium. It is now priced at about �26/gm. or $8000/lb. Lu'76 occurs naturally (2.6%) with Lu'75 (97.4%). It is radioactive with a halfAife of about 3 x 1010 yrs. Stable lutetium nuclides, which emit pure beta radiation after thermal neutron activation, can be used as a catalyst in cracking, alkylation, hydrogenation, and polymerization. Virtually no other commercial uses have been found yet for B-19 lutetium, as it is still one of the most costly natural elements. Lutetium, like other rare earth metals, has a low toxicity rating. It should be handled with care.

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