Lanthanide elements history

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 history of rare earth separations dates back to the discovery of yttria in the year 1794, and the isolation of ceria in 1803 after which a total of 17 rare earth elements. Sc, Y, La, Ac and the lanthanide elements (except Pm), were isolated laboriously (in varying degrees of purity) by relatively inefficient fractional precipitation methods, prior to 1947. Such methods have (for the most part) been outmoded by the development of more elegant counter-current techniques during the last 30 years. While the purpose of this chapter is to summarize and comment upon recent progress in means of isolating individual lanthanides and yttrium, some mention of well-developed processes for the preliminary treatment of rare earth mixtures must be made, to place the subject of component resolution in proper context. 

Krebs, Robert E. The history and use of our earth s chemical elements a reference guide. Westport (CT) Greenwood P, 1998. ix, 346p. ISBN 0-313-30123-9 A short history of chemistry — Atomic structure The periodic table of the chemical elements — Alkali metals and alkali earth metals - Transition elements metals to nonmetals — Metallics and metalloids - Metalloids and nonmetals — Halogens and noble gases - Lanthanide series (rare-earth elements) — Actinide, transuranic, and transactinide series... 

Figure 8.1 Periodic system, 1920s and 1930s. Prior to the 1940s, the lanthanides (rare-earths) were grouped separately as shown, but Th, Pa, and U (now classified as actinides), were considered to be transition elements, as shown in this table according to A. von Antropoff. From J. W. van Spronsen, The Periodic System of the Chemical Elements A History of the First Hundred Years (Amsterdam, 1969), fig. 59, p. 160.

The historical development of d- and f-hlock element chemistry also reflects their various chemical and physical properties. Metals occurring in elemental form were discovered early in human history, whereas chemically similar elements such as the lanthanides have only relatively recently been identified as separate elements. 

While the lanthanides (strictly defined as the 14 elements following lanthanum in the periodic table, but as normally used also include lanthanum itself) have several unique characteristics compared to other elements, their appearance in the history of the development of organometallic chemistry is rather recent. Since the f orbitals are filled gradually from lanthanum ([Xe]4f°) to lutetium ([Xe]4f14), they are regarded as the f-block elements, which are discriminated from the d-block transition elements. 

The uniform lanthanide pattern observed in crustal sediments on the earth, with its regular depletion in Eu, provides not only a key to the problem of sampling the continental crust, but also provides a crucial piece of evidence about crustal evolution. Eu is trivalent at the earth s surface, so that the observed depletion in upper crustal rocks recalls a previous history of the element as a divalent ion under more reducing conditions. It thus provides evidence that the upper crust of the earth resulted from production of granitic melts deep within the crust leading to retention of Eu in the deep crust, with a corresponding depletion at the present surface. 

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. 

Another important feature in the history of REEs was that they all were first extracted in the form of oxides. Chemists of the past used the name earths for oxides of, for instance, magnesium, calcium (cf. alkaline earths ) and applied it (erroneously, as it became clear later) to oxides of the first REEs, yttrium and cerium. Hence the term rare earths . Pure metals were prepared long after the discovery of the corresponding elements. For instance, a series of heavy lanthanides was prepared as pure metals only after the Second World War. Therefore, in our subsequent narration, the term REEs will refer to oxides. 

The lanthanide family of elements has played an important role which can be expected to continue in the development of coordination chemistry. In the early history of these elements, their close chemical similarity in the stable tripositive oxidation state made the task of achieving high purity for individual elements very difficult Although the entire lanthanide series had been discovered by 1907 (with the exception of Pm) and mixtures of lanthanides had been found in more than a hundred minerals, it was not until efficient separation methods were developed that detailed and diverse studies of their coordination chemistry could be undert en. 

As just mentioned, thirteen lanthanides had been discovered but, according to the new knowledge of the atom, one was missing. In 1914, Moseley confirmed that there must be an element with atomic number 61 between neodymium and samarium. Where was that element in nature Astronomical studies indicated that it is present on the surface of star in the Andromeda galaxy. But all attempts to find it on earth failed. The search had to take quite different paths than had been common in the whole history of lanthanide discovery. 

Gas-phase chemistry studies of atomic and molecular rare-earth and actinide ions have a deep-rooted history of more than three decades. In gas phase, physical and chemical properties of elementary and molecular species can be studied in absence of external perturbations. Due to the relative simplicity of gas-phase systems compared to condensed-phase systems, solutions or solids, it is possible to probe in detail the relationships between electronic structure, reactivity, and energetics. Most of this research involves the use of a variety of mass spectrometry techniques, which allows one exerting precise control over reactants and products. Many new rare earth and actinide molecular and cluster species have been identified that have expanded knowledge of the basic chemistry of these elements and provided clues for understanding condensed-phase processes. Key thermodynamic parameters have been obtained for numerous atomic and molecular ions. Such fundamental physicochemical studies have provided opportunities for the refinement and validation of computational methods as applied to the particularly challenging lanthanide and actinide elements. Among other applications, the roles of... 

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