Oganesson is a synthetic chemical element with the symbol Og and atomic number 118. It was first synthesized in 2002 at the Joint Institute for Nuclear Research (JINR) in Dubna, near Moscow, Russia, by a joint team of Russian and American scientists. In December 2015, it was recognized as one of four new elements by the Joint Working Party of the international scientific bodies IUPAC and IUPAP. It was formally named on 28 November 2016. The name honors the nuclear physicist Yuri Oganessian, who played a leading role in the discovery of the heaviest elements in the periodic table. It is one of only two elements named after a person who was alive at the time of naming, the other being seaborgium, and the only element whose eponym is alive as of 2023. Oganesson has the highest atomic number and highest atomic mass of all known elements. On the periodic table of the elements it is a p-block element, a member of group 18 and the last member of period 7. Its only known isotope, oganesson-294, is highly radioactive, with a half-life of 0. 7 ms and, as of 2020, only five atoms ever successfully produced. This has so far prevented any experimental studies of its chemistry. Because of relativistic effects, theoretical studies predict that it would be a solid at room temperature, and significantly reactive, unlike the other members of group 18 (the noble gases).

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Atomic properties

Atomic mass(294 u)

Atomic radii

Radius (empirical)(152 pm)
Covalent radius(157 pm)

Atomic shell

Electron configurationRn 5f14 6d10 7s2 7p6
Ionization energy(1st) (8.7 eV)
Shell model

Physical properties

Density(5.7 g·cm−3)
Molar volume(5.2·10-5 m3·mol−1)


Melting point(325 ±15 K)
Boiling point(450 ±10 K)
Liquid range(125 K)

Heat and conductivity

Thermal conductivity(0.0023 W·m-1·K-1)



Chemical properties

Oxidation state-

Other properties

Natural occurrencesynthetic
Crystal structureFace-centered cubic
Goldschmidt Classificationsynthetic
Radioactivityextremely radioactive