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As early as 1914, the possible existence of superheavy elements with atomic numbers well beyond that of uranium—then the heaviest known element—was suggested, when German physicist Richard Swinne proposed that superheavy elements around Z = 108 were a source of radiation in cosmic rays.
They considered elements 158 through 164 to be homologues of groups 4 through 10, and not 6 through 12, noting similarities of electron configurations to the period 5 transition metals (e.g. element 159 7d 4 9s 1 vs Nb 4d 4 5s 1, element 160 7d 5 9s 1 vs Mo 4d 5 5s 1, element 162 7d 7 9s 1 vs Ru 4d 7 5s 1, element 163 7d 8 9s 1 vs Rh 4d 8 5s 1 ...
A seventh possible isotope with mass number 294 has been reported but not yet confirmed. In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in group 16 as the heaviest chalcogen, but it has not been confirmed to behave as the heavier homologue to the chalcogen polonium.
The scientists involved in the discovery of element 118, as well as those of 117 and 115, held a conference call on 23 March 2016 to decide their names. Element 118 was the last to be decided upon; after Oganessian was asked to leave the call, the remaining scientists unanimously decided to have the element "oganesson" after him.
The heaviest element known at the end of the 19th century was uranium, with an atomic mass of about 240 (now known to be 238) amu. Accordingly, it was placed in the last row of the periodic table; this fueled speculation about the possible existence of elements heavier than uranium and why A = 240 seemed to be the limit
No undiscovered elements are expected to be stable; therefore, lead is considered the heaviest stable element. However, it is possible that some isotopes that are now considered stable will be revealed to decay with extremely long half-lives (as with 209 Bi). This list depicts what is agreed upon by the consensus of the scientific community as ...
Hassium is a synthetic chemical element; it has symbol Hs and atomic number 108. It is highly radioactive: its most stable known isotopes have half-lives of about ten seconds. [a] One of its isotopes, 270 Hs, has magic numbers of protons and neutrons for deformed nuclei, giving it greater stability against spontaneous fission.
The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences.