Actinides and Transactinides

Abstract

The actinide elements are a group of chemically similar elements with atomic numbers 89 through 103, and include actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium. Each of the elements has a number of isotopes, all radioactive. Thorium, uranium, and plutonium are well known for their role as the basic fuels (or sources of fuel) for the release of nuclear energy. The importance of the remainder of the actinide group lies at present in research. The actinides present a storage‐life problem in nuclear waste disposal. Only the members of the actinide group through Pu have been found to occur in nature. Thorium and uranium occur widely in the earth's crust in combination with other elements, and, in the case of uranium, in significant concentrations in the oceans. With these exceptions, the actinide elements are synthetic in origin for practical purposes, ie, they are products of nuclear reactions. All the actinide elements are radioactive, and, except for thorium and uranium, special equipment and shielded facilities are usually necessary for their manipulation. Special techniques for experimentation with the actinide elements other than Th and U have been devised because of the potential health hazard to the experimenter and the small amounts available. The actinide elements exhibit uniformity in ionic types. Corresponding ionic types are similar in chemical behavior, although the relative stabilities differ from element to element. Of the actinide ions, the small, highly charged \documentclass{article}\pagestyle{empty}\begin{document}${{\rm{M}}{^{4+}}}$\end{document} ions exhibit the greatest degree of hydrolysis and complex ion formation. The actinide metals, like the lanthanide metals, are highly electropositive. They can be prepared by the electrolysis of molten salts or by the reduction of a halide with an electropositive metal, such as calcium or barium. Thousands of compounds of the actinide elements have been prepared. 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. Nine such elements, numbers 104–1112, are now known, and evidence for the observation of elements 114, 116, and 118 was published in 1999. These reports now await confirmation. Thse elements are synthesized by the bombardment of heavy nuclides with heavy ions. Modern high‐speed computers have made possible the calculation of the electronic structure of the atoms, which gives some general guidance about chemical properties. Recently, the even more difficult theoretical problem of predicting the behavior of molecular species under actual experimental conditions has been addressed using relativistic quantum‐chemical calculations combined with fundamental physicochemical considerations.