in your element Peaceful berkelium The first new element produced after the Second World War has led a rather peaceful life since entering the period table — until it became the target of those producing superheavy elements, as Andreas Trabesinger describes.

f nomenclature were transitive, element 97 with the finding that in Bk(iii) compounds would be named after an Irish bishop spin–orbit coupling leads to a mixing of the Iwhose philosophical belief was that first excited state and the ground state. This material things do not exist. But between gives rise to unexpected electronic properties the immaterialist George Berkeley and the not present in analogous lanthanide element berkelium stands, of course, the structures containing terbium. Even more fine Californian city of Berkeley (pictured), recently5, a combined experimental and where the element was first produced in computational study revealed that berkelium December 1949. The city became the eponym can have stabilized +iii and +iV oxidation of element 97 “in a manner similar to that states also under mild aqueous conditions, used in naming its chemical homologue indicating a path to separating it from other terbium […] whose name was derived from lanthanides and actinides. the town of Ytterby, Sweden, where the rare The main use of berkelium, however — earth minerals were first found”1. arguably one that wouldn’t have met with A great honour for the city? The mayor Bishop Berkeley’s approval — remains a

of Berkeley at the time reportedly displayed PHOTO STOCK / ALAMY AF ARCHIVE distinctly material one: as the target for “a complete lack of interest when he was the synthesis of other transuranium and called with the glad tidings”2. There was every served as a helpful leitmotif. By the end of superheavy elements. For the production reason to take pride though. Berkelium was 1949, the team around Seaborg, including of element 117, which is currently the latest already the seventh new element discovered Albert Ghiorso and long-time collaborator addition to the periodic table, 249Bk samples in which the city’s University of California and schoolday friend Stanley Thompson, were produced at the Oak Ridge National Radiation Laboratory (later renamed the had finally succeeded and obtained trace Laboratory, Tennessee (US) in a procedure Lawrence Berkeley National Laboratory) was amounts of 243-berkelium by bombarding that takes well over a year6. Targets were critically involved. And by 1974, nine more 241-americium with helium ions. The path to then shipped to Dubna (Russia) and later elements would follow. the new kid on the f-block had been tedious, to Darmstadt (Germany), where they were Though an effort of many, one name so much so that Thompson and Ghiorso bombarded with 48-calcium to synthesize came to stand out in these elemental initially suggested assigning berkelium element 117. So crucial was the berkelium endeavours: Glenn Seaborg. A contributor the chemical symbol Bm — evoking target in these experiments that the name to the Manhattan project, he played a central an association with ‘bum’ — “because of element 117 references the place where role in the first synthesis of plutonium. it had been such a stinker in resisting the target — not the element itself — was The procedures developed for its chemical identification for so long”2. In the end produced: tennessine. ❐ isolation became crucial for the discovery though, Bk was adopted. of further transuranium elements. Elements Since its identification, berkelium led a ANDREAS TRABESINGER is a science 95 (americium) and 96 (curium) were still mostly tranquil life. The element has found writer based in Switzerland and the owner of produced during the war, but the next step no practical uses, although it can be formed Reinschrift Science Communication would prove tricky. in nuclear detonations and in nuclear (http://www.reinschrift.ch/). He has fallen Work towards synthesizing element 97 reactors. This makes understanding its in love with Berkeley during his postdoc started around Christmas 1945, but was chemistry relevant, in particular with a view years there. rendered difficult by the fact that only to nuclear-waste management. Yet, studying e-mail: [email protected] minute amounts of target materials were berkelium remains a challenge. Only one available for irradiation, and those were isotope is available in bulk quantities: 249Bk, References intensely radioactive. Nevertheless, Seaborg’s with a relatively short half-life of 330 days. 1. Thompson, S. G., Ghiorso, A. & Seaborg, G. T. Phys. Rev. recently postulated actinide concept (which Very early tracer experiments3 had shown 77, 838–839 (1950). 2. Seaborg, G. T. ChemTech 8, 408–413 (1978). posits that elements 89–103 form a series that berkelium has stable +iii and +iV 3. Thompson, S. G., Cunningham, B. B. & Seaborg, G. T. J. Am. of their own that mirror the lanthanides) oxidation states, but further properties of Chem. Soc. 72, 2798–2801 (1950). berkelium have only started to transpire in 4. Silver, M. A. et al. Science 353, 3762–3763 (2016). 5. Deblonde, G. J.‑P. et al. Nat. Chem. 9, 843–849 (2017). the past few years. In 2016, the first single- 6. Hamilton, J. H., Oganessian, Y. T. & Utyonkov, V. K. J. Phys. Conf. crystal structures were presented4, together Ser. 403, 012035 (2012). Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl 924 NATURE CHEMISTRY | VOL 9 | SEPTEMBER 2017 | www.nature.com/naturechemistry ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.