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Oganesson has the highest atomic number and highest atomic mass of all known elements as of 2024. 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.
Plutonium (Pu, atomic number 94), first synthesized in 1940, is another such element. It is the element with the largest number of protons (atomic number) to occur in nature, but it does so in such tiny quantities that it is far more practical to synthesize it. Plutonium is known mainly for its use in atomic bombs and nuclear reactors. [4]
Lighter isotopes of tennessine may be produced in the 243 Am+ 50 Ti reaction, which was considered as a contingency plan by the Dubna team in 2008 if 249 Bk proved unavailable; [101] the isotopes 289 Ts through 292 Ts could also be produced as daughters of element 119 isotopes that can be produced in the 243 Am+ 54 Cr and 249 Bk+ 50 Ti ...
One last possibility to synthesize isotopes near the island is to use controlled nuclear explosions to create a neutron flux high enough to bypass the gaps of instability at 258–260 Fm and at mass number 275 (atomic numbers 104 to 108), mimicking the r-process in which the actinides were first produced in nature and the gap of instability ...
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.
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).
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.