Lutetium (or lutetium) is a chemical element with
the Lu symbol and atomic number 71. It is the last element in the lanthanide
family and is counted among the rare earths.
Lutetium is a silvery gray, soft and ductile metal. Its applications are limited
due to its rarity and its high price. The production of this element indeed
requires to separate it from the other rare earths with which it is always
present.
Lutécium is a learned derivative of Lutèce (in Latin Lutetia), given by its
discoverer in honor of the city of Paris. In 1949, IUPAC changed the spelling of
the new element to lutetium2. In French, the spelling variant lutetium is
accepted, even if lutetium seems more common6.
Due to the debate over its discovery, the element has long been called
cassiopeium (symbol Cp) in German-speaking countries. This practice is now
obsolete.
Diagrams of rare earth discoveries. The dates in parentheses are the dates of
announcements of the discoveries7. The branches represent the separations of the
elements from an old one (one of the new elements retaining the name of the old,
except for the didyme).
Lutetium sublimated dendritics and 1 cm3 cube
Lutetium is the penultimate lanthanide to have been described, only promethium,
radioactive and unstable, was still unknown. It was discovered almost
simultaneously and independently by three chemists in 1907: The French Georges
Urbain, the Austrian Carl Auer von Welsbach and the American Charles James (in),
each of whom studied the ytterbine discovered in 1878 by Jean Charles Galissard
de Marignac, and was supposed to be composed of pure ytterbium oxide.
On November 4, 1907, Urbain showed the Paris Academy of Sciences that Marignac's
ytterbine was actually made up of two distinct elements. He proposed to name
them neo-ytterbium, "in order to avoid confusion with the old element of
Marignac", and lutetium, "derived from the old name of Paris" 8. A little later,
on December 19, 1907, von Welsbach announced that his work since 1905 on
fractional crystallization of ytterbium salts showed spectra proving the
existence of two distinct elements. He recommends the names cassiopeium (Cp,
after the constellation Cassiopeia, corresponding to lutetium) and aldebaranium
(Ad, after the star Aldebaran, replacing ytterbium) 9,10. At the same time, at
the University of New Hampshire, Charles James had been able to isolate
significant quantities of the ytterbium companion during the summer of 1907.
Upon learning of the announcement made by Georges Urbain, he gave up claiming
the authorship of the new element. However, among the three scientists, he was
probably the one with the most advanced research11.
During the years that followed, Urbain and von Welsbach fought for the
authorship of the discovery in a conflict exacerbated by political tensions
between France and Austria-Hungary. In 1909, the International Atomic Weight
Commission finally gave precedence to the lutetium of Georges Urbain (spelled
lutetium), while retaining the name ytterbium for the second element. Until the
1950s, many German-speaking chemists continued to use the term cassiopeium11.
Characteristics
Physical properties
Compact hexagonal crystal structure (hcp) of lutetium
a = 351.6 pm, c = 557.3 pm12.
The lanthanide contraction phenomenon makes lutetium the smallest element in
this family (atomic radius of 175 pm), while it has the highest atomic number.
As a result, it also shows the highest density (9.84 g · cm-3), melting point
(1,663 ° C) and boiling point (3,402 ° C) of all the lanthanides2.
The physical and structural properties of lutetium show many similarities with
the transition metals, in particular with scandium and yttrium. Despite these
considerations, lanthanum has long been placed under yttrium in the periodic
tables as the first element of block d, while lutetium was indicated as the last
element of block f. This is partly due to errors in the assessment of the
electronic configuration of these elements. More recent spectroscopic studies
have shown that the 71 electrons of the lutetium are arranged according to the
configuration [Xe] 4f145d16s2. When it enters a chemical reaction, the atom
loses the three elements
rhenium germanium zirconium cadmium hafnium
barium lithium beryllium strontium calcium
Tantalum gadolinium samarium yttrium ytterbium
Lutetium praseodymium holmium erbium thulium dysprosium
terbium europium lanthanum cerium neodymium scandium