Actinide concept

It was Seaborg who proposed the actinide concept it has become generally accepted practise to call the 15 elements beginning with Ac the actinide elements. However, we have to notice that, although immediately following lanthanum the 4f orbitals become more favourable than the 5d for the entrance of further electrons in the following elements there is not (until later) a similar situation for the 5f-6d... 

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]. 

These are listed in Table 20-11. While their preparations and properties show much similarity to those of the uranium halides, there is a steady decrease in stability of the higher oxidation states with increasing atomic number (which continues in the succeeding elements). In short, the actinide concept becomes more and more valid. 

SDS. See Sodium dodecyl sulfate Seaborg s actinide concept, 75 Secondary... 

Seaborg, G. T. 1994. Origin of the actinide concept. In Handbook on the physics and chemistry of rare earths. Vol. 18, Ixmlhanides/actinides chemistry, ed K. A. Gschneider, L. Eyring, G. R. Choppin, and G. H. Lander, pp. 1-27. New York Elsevier Science. 

Abstract This chapter reviews the historical perspective of transuranium elements and the recent progress in the production and study of nuclear properties of transuranium nuclei. Exotic decay properties of heavy nuclei are also introduced. Chemical properties of transuranium elements in aqueous and solid states are summarized based on the actinide concept. For new application of studying transuranium elements, an X-ray absorption fine structure (XAFS) method and computational chemistry are surveyed. 

To identify the new nuclide, a rapid cation-exchange separation technique using ammonium citrate as an eluant was employed. Early experiments indicated that element 97 had two oxidation states 3+ and 4+. The actinide concept provided the guidance to search for these two oxidation states, by analogy with the homolog element, terbium (Tb). The chemically separated samples were subjected to the measurement of radiation. Characteristic Cm X-rays associated with the electron capture (EC) decay and low-intensity a particles with a half-life of 4.5 h were detected. Berkelium was named after the city of Berkeley, California where it was discovered, just as the name terbium derived from Ytterby, Sweden. 

O Table 18.10 shows ionic radii of actinide elements together with those of lanthanide elements (Seaborg and Loveland 1990). The usefiil data on the ionic radii and coordination number are given by Shannon and Prewitt (1969). They carried out comprehensive study of crystal, or ionic, radii by analyzing the crystal structures of many fluoride, oxide, chloride, and sulfide compounds. Marcus published a data book on the properties of ions (Marcus 1997). The book covers a wide range of information on ionic radii of the actinide elements and other ions. Ionic radii of actinide elements decrease with increasing atomic number. This behavior is called actinide contraction and is one of the important examples of the actinide concept. 

---