Lutetium discovery

The lanthanides comprise the largest naturally-occurring group in the periodic table. Their properties are so similar that from 1794, when J. Gadolin isolated yttria which he thought was the oxide of a single new element, until 1907, when lutetium was discovered, nearly a hundred claims were made for the discovery of elements... 

Nor was Mendeleev s revolutionary Periodic Table a help. When he first published his Periodic Table in 1869, he was able to include only lanthanum, cerium, didymium (now known to have been a mixture of Pr and Nd), another mixture in the form of erbia, and yttrium unreliable information about atomic mass made correct positioning of these elements in the table difficult. Some had not yet been isolated as elements. There was no way of predicting how many of these elements there would be until Henry Moseley (1887-1915) analysed the X-ray spectra of elements and gave meaning to the concept of atomic number. He showed that there were 15 elements from lanthanum to lutetium (which had only been identified in 1907). The discovery of radioactive promethium had to wait until after World War 2. 

At nearly the same time, German chemist Karl Auer (Baron von Welsbach 1858—1929) made the same discovery. He suggested different names for the two new elements in ytterbium. He called them cassiopeium and aldebaranium, in honor of the constellation Cassiopeia and the bright star Aldebaran. Today, some German chemists still refer to lutetium as cassiopeium. 

A third chemist working on ytterbium was American chemist Charles James (1880—1926). James announced his discoveries after Urbain and Auer. Some authorities give credit for the discovery of lutetium to all three scientists. 

Nilson s analysis still did not solve this confusion. In 1907, French chemist Georges Urbain announced that Nilson s ytterbium was also a mixture of two new elements. Urbain called these elements ytterbium and lutetium. Marignac, Nilson, and Urbain are all given part of the credit for the discovery of ytterbium. 

Henry Moseley s discovery, in 1913, of the atomic number exposed gaps in the periodic table including those for missing elements 72 and 75. It is important to remember that lutetium, element number 71, the last rare earth element to be isolated, was reported only six years earlier. There were no guarantees that the lanthanides (elements 57-71) would not conceal yet one more surprise. And here the history of science also tantalizes Did theory predict experiment or did theory merely rationalize experiment ... 

The discovery of the rare earth elements started at the end of the 18th century. The first element to be discovered was Yttrium, by Finnish chemist and mineralogist Johan Gadolin (Gadolin 1794, 1796 Weeks 1968 Gupta and Krishnamurthy 2005). See Fig. 1.2 for a portrait of Gadolin. By the end of the 19th century, all but two of the rare earth elements had been discovered. Lutetium was discovered in 1907, and the last one (promethium) only after the discovery of nuclear reactions. Promethium was identified in 1947 (Marinsky et al. 1947). 

Lanthanum (Z = 57) and the following fourteen lanthanides from cerium (Z = 58) to lutetium (Z = 71) are usually classihed as rare-earth elements. Two more elements can be added to the list yttrium (Z — 39) and scandium (Z = 21) their properties are similar to those of lanthanum and they are linked historically with the rare earths. It was precisely the discovery of yttrium that began the history of rare-earth elements. Scandium, mentioned only briefly here, is considered in greater detail in Chapter 9. 

In total, the rare-earth elements (REEs) represent Vg of all the natural elements and their discoveries spanned 113 years—from 1794 (the discovery of yttrium) to 1907 (the discovery of lutetium). One of REEs, promethium, was prepared artificially much later. The unusual history of REEs is due to their extraordinary properties and, first of all, to their striking chemical similarity. In minerals and ores they are encountered all together at the same time, and it is extremely difficult to break the mixture into constituents. This made the history of REEs very rich in false discoveries with new elements often turning out to be mere combinations of already known ones. Even real discoveries did not always relate to pure rare-earth elements in many cases the newly discovered elements proved later to be a mixture of two or more unknown elements. That is why the widely accepted dates of the discovery of some REEs must be treated with a pinch of salt. 

Lutetium turned out to be the last natural REE and it ends the rare-earth series. Urbain was, however, of a different opinion. In 1911 he announced the discovery of a new element, celtium, placing it after lutetium in the periodic table. Later it became clear that the finding of celtium was in fact an experimental error. Urbain had interpreted its spectrum incorrectly the new lines in it were actually due to already known elements. 

Discovery Three scientists, G. Urbain in France, C. Auer von Welsbach in Austria and C. James in the USA investigated ytterbium carefully. In 1907, independently of each other, th discovered a new metal. Urbain called the new element lutecium after an old name for Paris. Auer wanted to use the name cassiopeium. In 1909 it was decided that the name should be lutetium. 

The two outer electron shells in neutral atoms of each lanthanide element have the same number of valence electrons as lanthanum, 2 and 1 respectively. This is the reason for the great similarities between them. And this is also the background to the enormously difficult discovery and separation work, characteristic of the lanthanides. But there are in fact some differences. In the third shell, the numbers of the so-called f-electrons differ. Lanthanum itself has no f-electron, the first lanthanide, cerium Ce, has 1, the second, praseodymium Pr, has 2 and the fourteenth, lutetium Lu, has 14 (see below, section 17.5.1). 

With rare earth metals he was more successful. He was originally inspired to research in this field by Lecoq de Boisbaudran, among others. Even ifhe had to sustain bitter fights with Auer, they ended with a recognized priority for the discovery of the element lutetium. 

During the period of discovery of the rare earths, which began with the separation of impure yttria by Gadolin in 1794 and ended with the discovery of the last stable rare earth lutetium by Urbain in 1907 (Weeks, 1968), research efforts were directed... 

---