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Probing Bohrium Bohrium Behaves Just As a Group 7 Element Should — but This Is in Fact Surprising, Philip Wilk Explains

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Probing Bohrium Bohrium Behaves Just As a Group 7 Element Should — but This Is in Fact Surprising, Philip Wilk Explains in your element Probing bohrium Bohrium behaves just as a group 7 element should — but this is in fact surprising, Philip Wilk explains. he superheavy element bohrium Over the course of many years and a few was first identified in 1981 at the different device iterations, the researchers GSI Helmholtz Centre for Heavy Ion constructed and tested a purpose-built T 1 Research in Darmstadt, Germany and was gas-phase chromatographic separator at the named after one of the founders of modern Paul Scherrer Institute in Switzerland. atomic and nuclear physics, Niels Bohr. During seminal investigations in Simply placing bohrium in group 7 of the 1999 and 2000, five atoms of267 Bh were periodic table would suggest a chemical identified by observing their distinctive behaviour similar to its above neighbour pattern of decay and chemically analysed4. rhenium — that is, if periodic trends were Although reaction parameters were to continue at the extreme end of the table. selected that favoured the longest-lived However it is not obvious that they should isotope, this isotope still decayed with a © HIPIX / ALAMY STOCK PHOTO © HIPIX / ALAMY STOCK and, in fact, theory suggests that they half-life of only ~17 s. Over two dozen must not. discarded 6d orbitals. The behaviour of scientists were involved in this scientific The now ubiquitous periodic table as these ‘superheavies’ is expected to be marathon to perform a volatility analysis proposed by Dmitri Mendeleev in 1869 was greatly influenced by relativistic effects, due on five individual atoms of bohrium. The arranged by increasing atomic weight, this to the tight binding of the inner electrons volatility was measured as adsorption original form was expanded to include that have velocities not far-removed from enthalpy of the oxychloride, and ultimately the noble gases and the lanthanides. It was the speed of light. These effects should determined that bohrium does in fact form then modified in 1913 by Henry Moseley to have such a profound effect on chemical an oxychloride — like the other group-7 arrange the elements by their X-ray energy bonding that traditional extrapolation elements technetium and rhenium. These (proportional to the square of the atomic of chemical properties down and across experiments further showed that the number), which solved the vexing problems the periodic table will be misleading at bohrium oxychloride is less volatile than of a few elements appearing out of sync with some point. Chemical studies on the rhenium oxychloride, which is in turn less their chemical properties. Tellurium and heaviest members of the table are therefore volatile than its technetium analogue. iodine, for example, swapped position, thus important, to test these theoretical What is rather surprising is that falling into place with the groups they were predictions and determine the influence of this result is thoroughly in line with expected to belong to. the relativistic effects. Such investigations predictions based purely on bohrium’s The next — and so far final — change have shown that the chemical behaviour position at the bottom of group 7 in the to the table was made in 1944 when of dubnium (element 105), for example, periodic table — despite the expected Glenn Seaborg postulated the existence does not rigorously follow trends down the breakdown of periodic trends as the of the actinide series analogous to the fifth group. relativistic effects dominate the chemical lanthanide series2 instead of a uranium-like Those chemical studies at the extreme behaviour of the heaviest of elements, group, which was the prevailing wisdom of end of the periodic table are challenging supported by the peculiar behaviour of the time. By this date, the basic chemistries to perform, due to the low production rate other transactinide elements, such as the of neptunium and plutonium were fairly of these elements. To reach the superheavy previously mentioned dubnium. ❐ well understood, and the initial chemical elements, heavy elements are bombarded experiments on as-yet-unnamed elements with lighter ones, resulting in (on rare References 95 and 96 were being carried out. Seaborg occasions) the complete fusion of target and 1. Münzenberg, G. et al. Z. Phys. A 300, 107–108 (1981). 2. Seaborg, G. T. Chem. Eng. News 23, 2190–2193 (1945). interpreted the existing evidence as projectile nuclei with production rates of an 3. Türler, A. Eichler, R. & Yakushev, A. B. Nucl. Phys. A indicating decidedly non-transition-metal- atom a day, or less. 944, 640–689 (2015). like behaviour, which pointed toward Starting in the late 1990s, Robert Eichler, 4. Eichler, R. et al. Nature 407, 63–65 (2000). the filling of the 5f orbitals instead of Heinz Gäggler, and a host of international the 6d ones. collaborators set upon the task of PHILIP WILK works for the Office of Basic With the end of the actinide elucidating the chemistry of bohrium Energy Sciences, US Department of Energy. series comes a transition metal series and other superheavy elements. The only The opinions in this essay are those of the characterized by filling these previously chemical or physicochemical method that author and do not represent the views or has the sufficient speed and efficiency to position of the US Department of Energy or achieve a chemical determination on these the US Government. ultra-rare elements is gas chromatography3. e-mail: [email protected] Rf Db Sg Bh Hs Mt Ds Rg Cn 113 Fl 115 Lv 117 118 119 120 121 122 123 124 634 NATURE CHEMISTRY | VOL 8 | JUNE 2016 | www.nature.com/naturechemistry ©2016 Mac millan Publishers Li mited. All ri ghts reserved. .
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