The Elusive Element

However, shortly after this annoimcement two Italian chemists, Luigi Rolla (1882-1960) and Lorenzo Fernandes (1902-1977), who were working at the University of Florence, claimed to have discovered element 61 in monazite from Brazil two years before the Americans, back in 1924 (Rolla and Fernandes, 1926,1927a,b,c, 1928). All their results had been meticulously written dovm in two long papers, but they had decided not to 

Auer von Welsbach was another chemist who doubted the validity of fhe American results. Finally, the married couple, Ida Noddack (nee Tacke, 1896-1978) and Walter Noddack (1893-1960), embarked upon a quest for fhe element 61. Husband and wife were greatly stimulated by their recent discoveries of masurium and rhenium. The Noddacks, in collaboration with Berg, began their investigations with an enormous amount of rare-earfh minerals (Noddack ef al., 1925). They firsf of all produced a number of very pure samples of neodymium and samarium. They made use of the most sensitive and accurate methods of analysis of fhat time, allowing to detect element 61 if if were 10 million times more rare than neodymium and samarium. However, their work remained without success. 

It was the German theoretical physicist, Josef Maffauch (1895-1976), who proved Ida Noddack to be correct, when he proposed the Mattauch rule (also 

All the possible mass numbers between 142 and 150 are already taken by neod)Tnium (Z = 60) and samarium (Z = 62), so that no stable isotope is expected for element 61. They would all be radioactive, just as in the case of technetium (Z = 43). The Mattauch rule however was not capable of ascribing these radioactive isotopes a certain half-life. A number of uranium and thorium isotopes are also radioactive, but their half-lives are great enough so that one can still find them in nature. During that same year, in 1934, the American physicist and future Noble Prize winner, Willard Libby (1908-1980), discovered that neodymium is a (3 emitter (Libby, 1934). According to Soddy s displacement laws, this should imply that when neodymium decays, isotopes of element 61 should be formed. 

Due to these recent discoveries, chemists did not lose their faith and they still hoped to discover the element 61 in nature. But most of them realized that it would probably be more successful to synthesize the element artificially. Technetium, the first artificially prepared element, had been formed in 1937 in the Berkeley cyclotron (Perrier and Segre, 1937,1947). One year later, in July 1938, the American physicists Pool and Quill of the University of Ohio started bombarding a neodymium target with fast deuterons (Pool and Quill, 1938). They were hoping that the proton would be taken up by the neodymium nuclei, with the formation of element 61 as a consequence  

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The alkali metals form a homogeneous group of extremely reactive elements which illustrate well the similarities and trends to be expected from the periodic classification, as discussed in Chapter 2. Their physical and chemical properties are readily interpreted in terms of their simple electronic configuration, ns, and for this reason they have been extensively studied by the full range of experimental and theoretical techniques. Compounds of sodium and potassium have been known from ancient times and both elements are essential for animal life. They are also major items of trade, commerce and chemical industry. Lithium was first recognized as a separate element at the beginning of the nineteenth eentury but did not assume major industrial importance until about 40 y ago. Rubidium and caesium are of considerable academic interest but so far have few industrial applications. Francium, the elusive element 87, has only fleeting existence in nature due to its very short radioactive half-life, and this delayed its discovery until 1939. 

Coster and Hevesy were thus encouraged to search amongst the zirconium minerals for the elusive element and in 1923 announced its presence as evidenced by its X-ray spectrum. They called the metal hafnium after Hafnia or Copenhagen. It was found to be present in varying amounts in most zirconium minerals, being about one-tenth as abundant as zirconium. Alvite (Zr, Hf, Th) Si04 was found to be particularly rich. 

In the twenties theorists attempted to reconstruct this family, to visualize its composition if it had existed. This imaginary structure had positions for the isotopes of elements 85 and 87 (but not for the radon isotopes). But this direction of search did not bring results, too. Perhaps the elusive elements did not exist at all ... 

The last years in the period of discovery and the some 30 years following it saw several developments in separation techniques for example, the reduction process was introduced for certain rare earths. The variety of chemical methods developed was then applied on an ever increasing scale, sometimes to many kilograms of starting materials especially large amounts were used in the search for the elusive element 61. As examples of the compounds used in the large-scale separation of the rare earths by fractional crystallization, ammonium nitrates and ferrocyanides may be mentioned. Spectroscopic methods were applied to evaluate the success of the separation. A review of the often very laborious separation procedures has been presented by Prandtl (1938). 

Because only a small number of stable selenoketones exist, studies of their decomposition are scarce. Irradiation of dwerf-alkylselones with UV light in hydrogen-donating solvents affords diselenides (80CJC6 87MI1), and the selone 37 behaves likewise. A second path of photolysis involves extrusion of molecular nitrogen from 37 to yield eventually tetramethyl-allene and elemental selenium, probably via the elusive... 

Since fluorine is the most electronegative element, it should inductively destabilize carbocations. The stability of fluoromethyl cations in the gas phase decreases in the order CFH2+ > CF2H+ > CF3+ > CH3+. The trend in solution, however, could be different, due to solvent effects, ion pairing, and so on. Indeed, fluorine has been shown to provide stabilization for carbocations. The existence of CH3CF2+, in contrast to the elusive ethyl cation CH3CH2+, is a clear evidence that replacement of H atoms by F atoms provides stabilization for carbocations.524 Furthermore, it was found that in perfluorobenzyl cation C6F5CF2+ fluorine atoms in resonance positions (ortho and para) are more deshielded than those in meta positions.536 This indicates carbocation stabilization by back-donation. 

The elusiveness of stable compounds with a triple bond between two group 14 elements (see Section VI.A) makes their synthesis, isolation and characterization one of the holy grails of main-group chemistry. In view of the many experimental failures to produce such compounds, even as short-lived intermediates (except for a few successes, see Section VI.A), theory remains the only reliable source of information. Furthermore, the calculations can be used to develop and test ideas of how to stabilize this group of compounds, hopefully directing experimentalists to their synthesis and isolation. 

Although Macquer did not utilize Boerhaave s conception of instruments, he took the four elements not as quality-bearing, elusive principles, but as material bodies subject to experimental control. The ramifications of Boerhaave s efforts to reconcile the chemical and the physical properties of four elements become obvious in Macquer s discussion. Air was the fluid that we respired. It surrounded the globe. It was susceptible to condensation and rarefaction caused by heat or cold (that is, by the presence or absence of the parts of fire). This gave it elas-... 

Many astrophysical textbooks accept the hypothesis of Michaud [14] of efficient stratification in the photosphere of selected elements, and even isotopes, by a delicate balance between the radiative pressure on the atoms and monatomic cations absorbing the ambient photons, and the fall due to gravitational attraction. This theory still needs to be refined in many elaborate details. If it applies to the He stars (Sect. 5) with the elusive helium isotope enriched by a factor 5000, the discrimination originates in the gravitational force being 25... 

The techniques of the Elus Cohen of Martinez de Pascuallis comprise three distinct elements ... 

Another informative aspect of this analogy is the issue of how to deal with the treatment of hierarchical level. Clearly, the chemical elements are made up of smaller particles (e.g., protons, neutrons, and electrons). Physicists have identified even smaller, more elusive entities such as bosons, quarks, and so on. Do we need to consider items at this lowest level of abstraction each time a simple compound such as hydrochloric acid is made Likewise, the term basic in basic elements of performance is clearly relative and requires the choice of a particular hierarchical level of abstraction for the identification of systems or basic functional units a level which is considered to be both natural and useful for the purpose at hand, lust as it is possible but not always necessary or practical to map chemical elements down to the atomic particle level, it is possible to consider mapping a basic element of performance (see latter) such as elbow flexor torque production capacity down to the level of muscle fibers, biochemical reactions at neuromuscular junctions, and so forth. 

Then Winkler made an assumption that the elusive amount had to be an unknown element. Inspired by the idea he began to study the mineral carefully and in February 1886 the principal events in the discovery of eka-silicon took place. 

Starting from 1913 scientists from various countries had been searching intensely for the elusive rare-earth element and it seemed strange that they had not found it earlier. Indeed, the elements of the first half of the rare-earth family known as the cerium elements (from lanthanum to gadolinium) had been shown by geochemists to be more abundant in nature than the yttrium elements of the second half of the family (from terbium to lutecium). But all the yttrium elements had been found while an empty box had remained in the cerium group between neodymium and samarium. 

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