Experimental studies. One-atom-at-a-time techniques

The placement of a new element in the Periodic Table requires knowledge of its atomic number and electronic configuration. Even though the atomic number can be positively assigned by a-decay chains, no knowledge is obtained about the electronic configuration or chemical properties of a new element fi om these physical methods. The elements are just placed in the Periodic Table by atomic number in various groups or series based on simple extrapolation of known Periodic Table trends or firom theoretical calculations and predictions of the electronic structures. It remains to the experimental chemist to attempt to validate or contradict these predictions. 

Fundamental properties used to judge similarities between newly produced elements and their lighter homologs are ionic radii (IR), stable oxidation states and complex formation. Since relativistic effects influence them all, the study of such effects is essential. It is important to establish to which extent relativistic effects in the heaviest elements influence the chemistry of their compounds, and whether deviations from known periodicities can be observed. 

chemical experiments must be carefully chosen with respect to a specific property which is strongly influenced by relativistic effects such that major changes could be detected [41]. The heat of formation of a heavy-element 

It turned out, however, that it is impossible to stabilize the heaviest 6d elements in the atomic state, which would require temperatures much above 1000 °C. Therefore, volatile halides and oxyhalides had to be used. In this case, the influence of relativistic effects on AHads or Tads becomes more complicated, since those quantities are complex functions of many single parameters, with individual contributions often cancelling out. The only way to study relativistic effects in this case is to compare experimental behaviour with that predicted on the basis of relativistic versus nonrelativistic calculations. 

The chemistry of elements 104 through 106 has successfully been studied on this atom-at-a-time basis (see Refs. 11-14 for reviews). Recently, the chemistry of bohrimn (element 107) has been investigated for the first time by using an isothermal gas-phase system [15] and the first chemical studies of element 108 (hassium) have been reported [16]. Experiments with even heavier elements such as 112 [17] are imderway and others are planned as well. Complete overviews of the experimental procedures and results can be found in Ref. 46. 

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