Chemical characterization of bohrium (element 107)

The arrangement of the chemical elements in the periodic table highlights r esemblances in chemical properties, which reflect the elements' electronic structure. For the heaviest elements, however, deviations in the periodicit y of chemical properties are expected(1-3): electrons in orbitals with a hi gh probability density near the nucleus are accelerated by the large nuclea r charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of t he nuclear charge and corresponding destabilization of the outer d and f or bitals: it is these changes that can give rise to unexpected chemical prope rties. The synthesis of increasingly heavy elements(4-6), now including tha t of elements 114, 116 and 118, allows the investigation of this effect, pr ovided sufficiently long-lived isotopes for chemical characterization are a vailable(7). In the case of elements 104 and 105, for example, relativistic effects interrupt characteristic trends in the chemical properties of the elements constituting the corresponding columns of the periodic table(8), w hereas element 106 behaves in accordance with the expected periodicity(9-12 ). Here we report the chemical separation and characterization of six atoms of element 107 (bohrium, Bh), in the form of its oxychloride. We find that this compound is less volatile than the oxychlorides of the lighter elemen ts of group VII, thus confirming relativistic calculations(13) that predict the behaviour of bohrium, like that of element 106, to coincide with that expected on the basis of its position in the periodic table.