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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 .
Oganesson (118 Og) is a synthetic element created in particle accelerators, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first and only isotope to be synthesized was 294 Og in 2002 and 2005; it has a half-life of 0.7 milliseconds.
Radon has no stable isotopes; its longest-lived isotope, 222 Rn, has a half-life of 3.8 days and decays to form helium and polonium, which ultimately decays to lead. [13] Oganesson also has no stable isotopes, and its only known isotope 294 Og is very short-lived (half-life 0.7 ms). Melting and boiling points increase going down the group.
In nuclear physics, the island of stability is a predicted set of isotopes of superheavy elements that may have considerably longer half-lives than known isotopes of these elements. It is predicted to appear as an "island" in the chart of nuclides , separated from known stable and long-lived primordial radionuclides .
Main isotopes of oganesson; Main isotopes [1] Decay; abundance half-life (t 1/2) ... It contains a table of main isotopes and eventually the standard atomic weight.
Of the 26 "monoisotopic" elements that have only a single stable isotope, all but one have an odd atomic number—the single exception being beryllium. In addition, no odd-numbered element has more than two stable isotopes, while every even-numbered element with stable isotopes, except for helium, beryllium, and carbon, has at least three.
Elements beyond the actinides were first proposed to exist as early as 1895, when Danish chemist Hans Peter Jørgen Julius Thomsen predicted that thorium and uranium formed part of a 32-element period which would end at a chemically inactive element with atomic weight 292 (not far from the 294 for the only known isotope of oganesson).
While the method of chemical characterization of a daughter was successful for flerovium and livermorium, and the simpler structure of even–even nuclei made confirmation of oganesson (Z = 118) straightforward, there have been difficulties in establishing the congruence of decay chains from isotopes with odd protons, odd neutrons, or both.