Actinides discovery

Ion exchange (qv see also Chromatography) is an important procedure for the separation and chemical identification of curium and higher elements. This technique is selective and rapid and has been the key to the discovery of the transcurium elements, in that the elution order and approximate peak position for the undiscovered elements were predicted with considerable confidence (9). Thus the first experimental observation of the chemical behavior of a new actinide element has often been its ion-exchange behavior—an observation coincident with its identification. Further exploration of the chemistry of the element often depended on the production of larger amounts by this method. Solvent extraction is another useful method for separating and purifying actinide elements. 

The elements beyond the actinides in the Periodic Table can be termed the transactinides. These begin with the element having atomic number 104 and extend, in principle, indefinitely. Although only six such elements, numbers 104—109, were definitely known in 1991, there are good prospects for the discovery of a number of additional elements just beyond number 109 or in the region of larger atomic numbers. They are synthesized by the bombardment of heavy nucHdes with heavy ions. 

Elements 43 (technetium), 61 (promethium), 85 (astatine), and all elements with Z > 92 do not exist naturally on the Earth, because no isotopes of these elements are stable. After the discovery of nuclear reactions early in the twentieth century, scientists set out to make these missing elements. Between 1937 and 1945, the gaps were filled and three actinides, neptunium (Z = 93), plutonium (Z = 94), and americium (Z = 95) also were made. 

Metal hydrides and acyl-like CO insertion products are two types of species likely to be present in any homogeneous or heterogeneous process for the catalytic reduction of carbon monoxide. The discovery and understanding of new types of reactivity patterns between such species are of fundamental interest. As discussed elsewhere (11,22,54-57), bis(pentamethylcyclo-pentadienyl) actinide hydrides (58) are highly active catalysts for olefin hydrogenation as well as H-H and C-H activation. 

Seaborg, G.T. The synthetic actinides - from discovery to manufacture, Amer. Nucl. Soc., San Francisco, Calif., Dec. 2,1969... 

The chemistry of neptunium (jjNp) is somewhat similar to that of uranium (gjU) and plutonium (g4Pu), which immediately precede and follow it in the actinide series on the periodic table. The discovery of neptunium provided a solution to a puzzle as to the missing decay products of the thorium decay series, in which all the elements have mass numbers evenly divisible by four the elements in the uranium series have mass numbers divisible by four with a remainder of two. The actinium series elements have mass numbers divisible by four with a remainder of three. It was not until the neptunium series was discovered that a decay series with a mass number divisible by four and a remainder of one was found. The neptunium decay series proceeds as follows, starting with the isotope plutonium-241 Pu-24l—> Am-24l Np-237 Pa-233 U-233 Th-229 Ra-225 Ac-225 Fr-221 At-217 Bi-213 Ti-209 Pb-209 Bi-209. 

The first actinide metals to be prepared were those of the three members of the actinide series present in nature in macro amounts, namely, thorium (Th), protactinium (Pa), and uranium (U). Until the discovery of neptunium (Np) and plutonium (Pu) and the subsequent manufacture of milligram amounts of these metals during the hectic World War II years (i.e., the early 1940s), no other actinide element was known. The demand for Pu metal for military purposes resulted in rapid development of preparative methods and considerable study of the chemical and physical properties of the other actinide metals in order to obtain basic knowledge of these unusual metallic elements. 

For non-magnetic actinide metals, specific heat data have been employed very usefully to corroborate 5 f localization starting with Am, as indicated by the sudden drop in y values (ypu 12 mJ/mol K, yAm 2 mJ/mol K ). It allowed also the discovery of superconductivity in Pa and Am metals ... 

FERMIUM. ICAS 7440-72-4). Chemical element symbol Fm. at. no. 100. at. wt. 257 (mass number of the most stable isotope), radioactive metal of the Actinide series, also one of the Transuranium elements. During Ihe period 1953- 1954. a group of scientists at the Nobel Institute of Physics (Stockholm) bombarded U with l60 ions, producing and isolating a 30-min alpha emitter. Ibis was called -5"l(X). However, discovery of element 100 was noi claimed at that time. Subsequently, the isotope was identified and the 30-miu half-lile conlirmed. Both fermium and einsteinium were formed in a thermonuclear explosion that occurred in the South Pacific in 1952. The elements were identified by scientists from the University of California s Radiation Laboratory, the Argonne National Laboratory, and die Los Alamos Scientific Laboratory. It was observed that very heavy uranium isutopes lhal resulted from the action of the instantaneous neutron flux cm uranium (conlaincd in the explosive device) decayed lo form Es and Fm, The probable electronic configuration of... 

The years after World War II led to the discovery of elements 97-103 and the completion of the actinide series. While the story of the discovery of each of these elements is fascinating, we shall, in the interests of brevity, refer the reader elsewhere (see References) for detailed accounts of most of these discoveries. As an example of the techniques involved, we shall discuss the discovery of element 101 (mendelevium). 

Contemporaneously with the Berkeley experiments, Zvara et al. (1969, 1970), working at Dubna, produced 3.2 + 0.8 s 259104 by the Pu/ Ne, 5n) reaction. The chloride of this spontaneously fissioning activity was shown using gas chromatography to be slightly less volatile than Hf, but more volatile than the actinides. An international group of reviewers (Barber et al., 1992) has determined that the Berkeley and Dubna groups should share the credit for the discovery of element... 

Dam, H.H., Beijleveld, H., Reinhoudt, D.N., Verboom, W. 2008. In the pursuit for better actinide ligands An efficient strategy for their discovery. Journal of the American Chemical Society 130(16) 5542-5551. 

Usually the discovery of a new element is announced in a scientific paper or at a scientific meeting. The actinide elements curium and americium were announced to the world in a 1945 childrens radio show called Quiz Kids. The show s guest scientist on November 11 that year was a young scientist named Glenn Seaborg. One of the children on the show asked Seaborg if any new elements had been discovered lately. Seaborg happily shared the news that his lab had in fact created two new elements with atomic numbers 95 and 96. 

There is nothing like the development of the periodic table through time to give one a sense of the pace of chemical discovery. Lavoisier listed close to thirty elements, and this number more than doubled when Mendeleev invented the periodic table. Since then, we have added the lanthanides and actinides, as well as a stream of artificial radioactive elements. 

When G. T. Seaborg in 1944 introduced his actinide concept the theory played not the last role in his decision to place newly discovered elements in a second series where the filling of the 5f-shell takes place, similarly to the lanthanide series where the filling of the 4f-shell takes place. Thus, the filled-shell concept was in accord with the newly found periodicity in chemical properties and resulted in the discovery of all the heavy actinides at that time [20]. 

With almost all of the conceivable coordination chemistry of the expanded porphyrins still left to be explored, it cannot be over-stres that the potential for new chemistry is enormous. This is i rticularly true when account is made of the fact that the chemistry of the metalloporphyrins has played a dominant role in modern inorganic chemistry. What with the possibility to enhance the stability of imusual coordination geometries (and, perhaps oxidations states) and the ability to form stable coordination complexes with a variety of unusual cations including those of the lanthanide and actinide series, the potential for new inorganic and organometallic discoveries are almost unlimited. For instance, as with the porphyrins, one may envision linear arrays of stacked expanded porphyrin macrocycles which may have unique conducting properties and/or which could display beneficial super- or semiconducting capabilities. Here, of course, the ability to coordinate not only to cations but also to anions could prove to be of tremendous utility. 

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