Since the discovery of nuclear fission in 1938, scientists have artificially produced 26 elements and hundreds of isotopes, all by using nuclear reactions (see the article by Yuri Oganessian and Krzysztof Rykaczewski, Physics Today, August 2015, page 32). For the newly created elements, their lifetimes are often so short—and their yields so low—that their chemical and physical properties cannot be analyzed experimentally. Researchers must instead turn to atomic calculations. Oganesson, the most recent addition to the periodic table, has an atomic number of 118 and a half-life of less than a millisecond. It’s also the heaviest element ever created and the only superheavy element (one whose atomic number exceeds 103) in the column of noble gases. Because of the large nuclear charge, inner-shell electrons orbit at near light speed, and their relativistic effects, notably spin–orbit coupling, are especially important. Og’s electron structure is expected to differ significantly from that found in lighter elements whose electrons are concentrated in discrete shells and subshells.
Using calculations based on the Dirac equation, Paul Jerabek, a postdoc at Massey University in Auckland, New Zealand, and his colleagues have now borne out that expectation. They find that electrons in Og are spread out into a delocalized, nearly uniform-density distribution that resembles a so-called Thomas–Fermi gas of noninteracting particles. The team obtained that result essentially by calculating the probability of finding electrons close to each other. In contrast to that of its two closest noble-gas neighbors xenon and radon, the shell structure in Og is barely discernable in the figure, which plots the electrons’ spatial localization on a scale from 0 to 1. The upshot: Although its number of electrons dictates that Og has a closed-shell configuration, it is likely to be more reactive than one would expect for a noble gas. (P. Jerabek et al., Phys. Rev. Lett. 120, 053001, 2018.)