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Chemical characterization of bohrium (element 107)

Abstract

The arrangement of the chemical elements in the periodic table highlights resemblances in chemical properties, which reflect the elements’ electronic structure. For the heaviest elements, however, deviations in the periodicity of chemical properties are expected1,2,3: electrons in orbitals with a high probability density near the nucleus are accelerated by the large nuclear charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of the nuclear charge and corresponding destabilization of the outer d and f orbitals: it is these changes that can give rise to unexpected chemical properties. The synthesis of increasingly heavy elements4,5,6, now including that of elements 114, 116 and 118, allows the investigation of this effect, provided sufficiently long-lived isotopes for chemical characterization are available7. 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 table8, whereas element 106 behaves in accordance with the expected periodicity9,10,11,12. 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 elements of group VII, thus confirming relativistic calculations13 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.

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Figure 1: The six nuclear decay chains of 267Bh leading to 263Db and 259Lr.
Figure 2: Results of isothermal gas adsorption chromatographic separations of group VII metal oxychlorides in quartz columns.

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Acknowledgements

We are indebted to the Office of Science, Office of Basic Energy Research, Division of Chemical Sciences, of the US Department of Energy, for making the 249Bk target material available through the transplutonium element production program at the Oak Ridge National Laboratory. We thank the staff of the PSI Philips cyclotron for providing intense beams of 22Ne. This work was supported in part by the Office of Science, Office of High Energy and Nuclear Physics, Division of Nuclear Physics, of the US Department of Energy and by the Swiss National Science Foundation.

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Eichler, R., Brüchle, W., Dressler, R. et al. Chemical characterization of bohrium (element 107). Nature 407, 63–65 (2000). https://doi.org/10.1038/35024044

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