TRANSURANIUM ELEMENT

Figure 1: Modern version of the periodic table of the elements. To see more information about an any of the chemical elements that lie beyond uranium in the periodic table (see Figure)i.e., those with atomic numbers greater than 92. Twenty of these elements, up to and including atomic number 112, have been discovered. Eleven of them, from neptunium through lawrencium, belong to the actinide series (see actinide element). The other nine, which have atomic numbers higher than 103, are referred to as the transactinides. All the transuranium elements are unstable, decaying radioactively, with half-lives that range from tens of millions of years to mere fractions of a second. Since only 2 of the 20 have been found in nature (neptunium and plutonium) and those only in trace amounts, the synthesis of these elements through nuclear reactions has been an important source of knowledge about them. That knowledge has expanded scientific understanding of the fundamental structure of matter and makes it possible to predict the existence and basic properties of elements much heavier than element 112. Present theory suggests that the maximum atomic number could be found to lie somewhere between 170 and 210, if nuclear instability would not preclude the existence of such elements. All these still-unknown elements are included in the transuranium group. any of the chemical elements that lie beyond uranium in the periodic tablei.e., those with atomic numbers greater than 92. All the transuranium elements are radioactive. They have half-lives ranging from tens of millions of years to fractions of a millisecond. Of the known transuranium elements, only neptunium and plutonium have been found in nature. Both occur only in minute amounts, however. The other elements have been synthesized through various nuclear reactions. These reactions involve transmuting the atoms of one element into those of another by bombarding the former with neutrons or fast-moving charged particles. This changes the number of protons in their nuclei (i.e., atomic number) to that of the new element. The transuranium elements are neptunium (93), plutonium (94), americium (95), curium (96), berkelium (97), californium (98), einsteinium (99), fermium (100), mendelevium (101), nobelium (102), lawrencium (103), unnilquadium (rutherfordium; 104), unnilpentium (hahnium, or dubnium; 105), unnilhexium (seaborgium; 106), unnilseptium (bohrium, or nielsbohrium; 107), unniloctium (hassium; 108), unnilennium (meitnerium; 109), ununnilium (110), unununium (111), and ununbium (112). The transuranium elements from neptunium (93) through lawrencium (103) are chemically similar to the rare-earth elements (see rare-earth metal). Elements with atomic numbers above 103 are often called transactinides. Those with atomic numbers 104 and 105 seem to be chemically analogous to the elements immediately above them in the periodic tablehafnium and tantalum, respectively. The chemical properties of the other transactinides are uncertain. Additional reading Two articles for the lay reader are Glenn T. Seaborg, The New Elements, American Scientist, pp. 279289 (MayJune 1980); and Glenn T. Seaborg and Justin L. Bloom, The Synthetic Elements: IV, Scientific American, 220:5767 (1969), fourth in a series that covers the field from its inception. Methods for preparing and characterizing short-lived heavy elements can be found in Peter Armbruster and Gottfried Mnzenberg, Creating Superheavy Elements, Scientific American, 260(5):6672 (May 1989); and Darleane C. Hoffman, The Heaviest Elements, Chemical & Engineering News, 72(18):2434 (May 2, 1994). More technical works include Glenn T. Seaborg, Man-Made Transuranium Elements (1963), suitable for scientifically inclined high school students and for college students; Glenn T. Seaborg (ed.), Transuranium Elements: Products of Modern Alchemy (1978), a collection of benchmark research papers; and Glenn T. Seaborg and Walter D. Loveland, The Elements Beyond Uranium (1990). Comprehensive works on the field include Earl K. Hyde, Isadore Perlman, and Glenn T. Seaborg, The Nuclear Properties of the Heavy Elements, 3 vol. (1964, reissued 1971); and Cornelius Keller, The Chemistry of the Transuranium Elements (1971). Glenn T. Seaborg