Extended periodic table

An extended periodic table places predicted or hypothetical elements beyond the currently confirmed elements in a periodic arrangement. Its proposed entries depend on models of nuclear stability and electron structure.

Island of stability: A predicted region of enhanced stability among superheavy nuclei, caused by closed proton or neutron shells. It offers the main reason some elements beyond known ones might have measurable lifetimes.
Aufbau principle: A rule of thumb that places electrons in available orbitals in order of increasing energy. Extrapolated orbital filling supplies the basis for many proposed table layouts.
Dmitri Mendeleev: A Russian chemist who formulated an influential periodic table and predicted properties of undiscovered elements. His willingness to leave gaps established a precedent for placing elements before discovery.
Standard periodic table: The conventional arrangement of confirmed elements, ordered by atomic number into periods and groups. It stops at confirmed elements, unlike extensions that include proposed entries.
Nuclear shell model: A model describing nucleons as occupying quantized energy levels within an atomic nucleus. Its predicted shell closures help estimate which unmade elements could resist decay.
Electron configuration: The distribution of an atom’s electrons among its orbitals and energy levels. Predicted configurations assign chemical character to elements that have not been observed.
Janet left-step periodic table: A periodic-table arrangement that places the s-block elements to the right of the f-block and groups orbitals by filling order. Its orbital-based geometry can yield a different extension beyond the known elements.
Long-form periodic table: A periodic-table layout that displays the lanthanides and actinides within their periods rather than as detached rows. This presentation choice affects how extensions accommodate the f-block.
Superheavy element: A chemical element with an atomic number substantially above that of naturally abundant elements, generally produced artificially. The extended table’s proposed entries belong to this broader class.
Periodic law: The principle that elemental properties recur periodically when elements are ordered by atomic number. The extended table assumes this recurring pattern continues beyond confirmed elements.

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