explored the electronic and nucleonic structure of oganesson, including the extent of localization. A similar transition-from a shell structure to a gas-like distribution-is expected to occur in the nuclei of heavy elements. As the number of electrons increases, strong localization is expected to smooth out into a distribution resembling a Thomas-Fermi gas, which is a hypothetical, uniform-density gas based on a quantum-mechanical model of electron pairing. For many elements, the electrons are located within specific shells that are separated by low-density bands. For example, it has been hypothesized that a transition will occur in the distribution (localization) of the electrons around the nucleus. There are other heavy-element behaviors that have been predicted but not yet observed. This can have significant impact upon the manifestation of chemical and physical properties in elements from the lower half of the periodic table-the most common examples are gold, whose color arises because of relativistic effects, and mercury, whose very low melting point can be attributed to the impact of relativity. As the atomic number increases, the impact of relativity also becomes more important, as inner-shell electrons move faster to avoid falling into the highly charged nucleus. For example, heavy elements experience lanthanide contraction, which is a shrinking of the atomic radius due to reduced shielding by inner-shell electrons of nuclear attractive forces on outer-shell electrons. It has long been known that the characteristics of the elements in the periodic table change significantly as the atomic number increases. This suggests that oganesson has chemical and physical properties that are very different from those of other noble gas elements. They found that both the electrons and nucleons have a uniform distribution, which is in stark contrast to the nonuniform shell structure seen in lighter elements. In a first for superheavy atoms, Paul Jerabek from Massey University Auckland, New Zealand, and colleagues have used fermion localization-a common method for visualizing electron or nucleon spatial distributions-to characterize the structure within oganesson. Instead, researchers must rely on atomic calculations to ascertain the fundamental properties of such a short-lived element. Oganesson has an estimated half-life of less than 1 ms, which is not enough time for most chemical observations. This intriguing new element, which was first synthesized in 2002, completes the seventh row (7 p block) of the periodic table and is the first superheavy ( Z > 1 0 3) noble gas element.Ī challenge in understanding oganesson and other superheavy elements is their short half-lives and low production rates. The most recent entry to this column is oganesson (Og), which is the element with the highest known atomic number ( Z = 1 1 8). An example is the late 19th century addition of a new column (group) of elements, the noble gases, by William Ramsay, who received the 1904 Nobel Prize in Chemistry for his discovery. There have been over 700 versions of the table of elements to date, with elements regularly being added, filling empty blocks of the table. The periodic table continues to evolve, as it has since the publication of the first widely recognized periodic table by Dmitri Mendeleev in 1869. This uniform behavior contrasts with the shell structure observed in lighter elements like xenon (Xe) and radon (Rn), shown in the top and middle panels. Theoretical calculations of the electronic structure of this heavy element (bottom right panel) show that the distribution of electrons is smooth, as one would expect for a gas of noninteracting particles. and APS/ Alan Stonebraker Figure 1: One of the latest additions to the periodic table is oganesson (Og).
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