Chemistry of the Elements Einsteinium through Element-105

Abstract

All known chemical properties of each of the elements 99 (Es) through 105 are reviewed and these properties are correlated with the electronic structure expected for 5/and 6 d elements. A major feature of the heavier actinides, which differentiates them from the comparable lanthanides, is the increasing stability of the divalent oxidation state with increasing atomic number. The divalent oxidation state first becomes observable in the anhydrous halides of californium and increases in stability through the series to nobelium, where this valency becomes predominant in aqueous solution. In this range of elements, the II -<· III oxidation potential decreases from ~ +1.5 to -1.5 volts. These observations lead to the conclusion that, in comparison with the analogous 4/electrons, the 5/ electrons in the latter part of the series are more tightly bound. Thus, there is a lowering of the 5/energy levels with respect to the Fermi level as the atomic number increases.The metallic state of the heavier actinides has not been investigated except from the viewpoint of the relative volatility among members of the series. In aqueous solutions, ions of these elements behave as "normal" trivalent actinides and lanthanides (except for nobelium). Their ionic radii decrease with increasing nuclear charge which is moderated because of increased screening of the outer 6 ρ electrons by the 5/electrons. These relative ionic radii have been obtained from comparisons of the elution position in chromatographic separations.Lawrencium (Lr) completes the actinide series of elements with an electronic configuration of 5 / 14 7 s J 7 p. From Mendeleev's periodicity and Dirac-Fock calculations, the next group of elements is expected to be a ¿/-transition series corresponding to the elements Hf through Hg. The chemical properties of elements 104 and 105 only have been studied and they indeed appear to show the properties expected of eka-Hf and eka-Ta. However, their nuclear lifetimes are so short and so few atoms can be produced that a rich variety of chemical information is probably unobtainable.

Chemistry at Low Concentrations: Polonium at a Level of 5000 to 40 Atoms

“…A coprecipitation reaction, for example, may involve many deposition-dissolution steps of the microcomponent atoms on the forming macroscopic solid and, hence, a multistep mechanism may be achieved to a sufficiently good approximation. In recent years, the question of the validity of single-atom chemistry came up again in connection with the chemical isolation and characterisation of the heaviest elements [1,2]. Such studies have often to be carried out on the basis of a few atoms per experiment.…”

Atom-at-a-Time Chemistry

“…As pointed out by Hulet [20] in a 1983 review, early investigations of the gas-phase chemistry of element 104 relied on detecting SF from the 3-sec 259 104, and make it difficult to assess the validity of these experiments. Subsequent investigations of the chemistry of element 104 utilized detection of alphas from the 65-sec 261 Rf produced via 248 Cm( 18 0,5n) reactions.…”

Chemistry of the Heavy Actinides and Light Transactinides

“…The undiscovered elements, eka-platinum through eka-radon, are shown in their predicted places [3]. Since elements above fermium must be produced on accelerators in one or a few atoms at a time quantities, most of the reliable chemical experiments in this region have been done using techniques that put each of the few available atoms through many reactions [2,3]. For example, in their pioneering investigations of the chemistry of Lr and Rf, SILVA, HULET, ZVARA, and their coworkers em· ployed ion exchange, solvent extraction, and gas chromatography [8,9,10,11,12], At the present time, our knowledge of the chemistry of the elements at the end of the periodic table is based on the four experiments performed by these investigators.…”

“…For example, expected production rates [1] for long lived isotopes of elements 102-105 are given in Table 1 for a 30 microgram 254 Es target and a 0.5 particle-microamp beam of 22 Ne. These production rates are 10 times those available today and are sufficient for experiments in ion exchange, solvent extraction, and gas chromatography such as have been successfully used for chemical studies on a "one atom at a time" basis in the past [2,3], In addition, the 155 neutrons of 2S4 Es, coupled with the 28 neutrons from a bombarding particle of 48 Ca, would give a compound nucleus of 183 neutrons -only one short of the magic number of 184 calculated for stabilization of a superheavy element [4]. If such a large 2 54 Es sample could be made, it would have to be produced at the High Flux Isotope Reactor/Transuranium Processing Plant (HFIR/TRU) complex in Oak Ridge.…”