The Elements beyond

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. 

On the basis of the simplest projections it is expected that the half-Hves of the elements beyond element 109 will become shorter as the atomic number is increased, and this is tme even for the isotopes with the longest half-life for each element. This is illustrated by Figure 6, in which the half-Hves... 

G. T. Seaborg and W. D. Loveland, The Elements Beyond Cranium, Wiley-Interscience, New York, 1990. 

Mt, Z = 109) were formally named in 1997. The transmeitnerium elements, the elements beyond meitnerium (including hypothetical nuclides that have not yet been made) are named systematically, at least until they have been identified and there is international agreement on a permanent name. Their systematic names use the prefixes in Table 17.2, which identify their atomic numbers, with the ending -him. Thus, element 110 was known as ununnilium until it was named darmstadtium (Ds) in 2003. 

The elements beyond Row 2 of the periodic table can accommodate more than four groups of electrons, and this results In steric numbers greater than 4. 

Seaborg GT, Loveland WD. 1990. The elements beyond uranium. New York John Wiley Sons, Inc. 

Isotopes of the elements beyond U are produced artificially, Np and Pu by neutron capture by U, Am and Cm by multiple neutron capture by Pu, and elements beyond Cm by further neutron captures or bombardment of lower atomic number actinoids with ions of He, B, C, N, or O. As the atomic number increases, the elements become more unstable and thus tend to have shorter half lives. Np-237 and Pu-239 are available in multikilogram amounts Am-241 (430 years), Am-243 (7650 years), and Cm-244 (18.1 years) in 100-g amounts Bk-249 (320 days), Cf-252 (2.6 years), and Es-253 (20 days), in milligram amounts Fm-257 in microgram quantities and Md-258 (55 days), No-259 (1.0 h), and Lr (3.0 min) in trace amounts. 

Seaborg, G.T. and W.D, Loveland The Elements Beyond Uranium, John Wiley Sons, New York, NY, 1990. 

The first scientific attempts to prepare the elements beyond uranium were performed by Enrico Fermi, Emilio Segre, and co-workers in Rome in 1934, shortly after the existence of the neutron was discovered. This group of investigators irradiated uranium with slow neutrons and found several radioactive products, which were thought to be due to new elements. However, detailed chemical studies by Otto Hahn and Fritz Strassman in Berlin showed these species were isotopes of the known elements created by the fission of uranium into two approximately equal parts (see Chap. 11). This discovery of nuclear fission in December of 1938 was thus a by-product of man s quest for the transuranium elements. 

Neptunium, the element beyond uranium, was named after the planet Neptune because this planet is beyond the planet Uranus for which uranium is named. 

All the elements beyond Z = 94 are synthetic and are produced by the bombardment of target nuclei with a smaller projectile. For example, German scientists have made two atoms of element 112, ununbiium (Uub), by bombarding lead-208 atoms with zinc-70 atoms in a heavy-ion accelerator ... 

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements beyond Uranium. New York Wiley. 

The continual evolution of the discipline of chemistry is reflected in our treatment of the elements. The careful reader will note that we have included articles for the first 104 elements the remainder of the elements are recently discovered or exist only as short-lived species and, accordingly, are not readily available for the usual chemical studies that reveal, for example, their bulk properties or reactivity and much of the standard chemistry that is of interest. Much of what little we know about the elements beyond 104 permits us to place these elements in their appropriate places in the periodic table, which nevertheless still turns out to be quite insightful from a chemical point of view. 

The chemistry of actinides is more complicated due to the existence of greater range of oxidation states for these metals. Moreover, all these metals are radioactive and therefore, their accessibility for laboratory investigations is limited. The elements beyond uranium are all man-made elements and are made by nuclear-chemical methods. 

Already many more elements have been synthesized than could be predicted in the early 1960s. Higher neutron-flux reactors could make the necessary amounts of the heavier transuranium elements needed for synthesis of the elements beyond 112. Much will depend upon whether the more neutron-rich isotopes with longer half-lives, essential for any study of chemical properties, can be made. The only safe prediction is the unpredictability of this area. 

G.T. Seaborg andW.D. Loveland, The Elements beyond Uranium, Wiley, 1990, pp. 71-78 (f electrons). 

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