Tennessine

Tennessine was first created in 2010 at the Joint Institute for Nuclear Research in Dubna, Russia, in collaboration with American laboratories, by fusing berkelium and calcium nuclei; the berkelium target was supplied by the Oak Ridge National Laboratory in Tennessee. It was named after the state of Tennessee. Tennessine is an intensely radioactive synthetic element, known only from a few atoms, and it is classed with the halogens. Its isotopes last only milliseconds and it has no studied chemistry; whether so heavy an atom truly behaves as a halogen is a question theory cannot yet fully answer, and its synthesis depended on a berkelium target that could be made in only one reactor in the world.

Producing the berkelium-249 target for tennessine's discovery was itself a race against the clock: the isotope has a half-life of only about 330 days, so after roughly 250 days of continuous irradiation at Oak Ridge's High Flux Isotope Reactor yielded just 22 milligrams of usable material, the sample had to be rapidly purified and shipped to Dubna, Russia, and used in the fusion experiment before too much of the hard-won target decayed away, a genuine logistical drama layered on top of the underlying nuclear physics.

Tennessine honours the American state of Tennessee, home to the Oak Ridge National Laboratory, the University of Tennessee and Vanderbilt University, whose contribution, above all the production of the rare berkelium target essential to the synthesis, made the element possible. Its name ends in -ine rather than the usual -ium, following the convention for the halogens, the family of fluorine, chlorine, bromine, iodine and astatine in which element 117 sits, though whether so heavy an element truly behaves like a halogen remains a theoretical question.

Tennessine was the last of the four elements whose confirmation in 2016 completed the seventh period of the periodic table, filling the final gap in the seven known rows. It has no ancient or esoteric tradition, being a synthetic element of the twenty-first century; its name marks the American laboratories' part in finishing the table. Theoretical calculations suggest tennessine might turn out to be the first metallic halogen, its heavy, relativistically distorted electron cloud predicted to give it a duller shine and a shift toward metal-like bonding quite unlike the volatile, sharply coloured lighter halogens fluorine, chlorine, bromine and iodine, though with atoms surviving only milliseconds, testing that prediction directly remains far beyond current experimental reach.