Untriseptium

Untriseptium is the temporary systematic name assigned to hypothetical chemical element 137. No element with atomic number 137 has been observed or confirmed.

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Atomic number: The number of protons in an atom’s nucleus, defining which chemical element it is. Element 137 would be defined by having 137 protons.
Extended periodic table: A proposed arrangement of elements beyond those currently confirmed, based on predicted atomic structure and periodicity. It places untriseptium among hypothetical elements beyond the known table.
Ununtrium: The former temporary systematic name for element 113, now officially named nihonium. Its replacement illustrates how a temporary name gives way after an element is confirmed.
Fine-structure constant: A dimensionless physical constant measuring the strength of electromagnetic interactions. Its value helps set the relativistic threshold associated with nuclear charge near 137.
IUPAC systematic element name: A temporary name formed from digit roots for an element whose permanent name has not been adopted. Untriseptium encodes the digits of atomic number 137 using this naming system.
Periodic table block: A region of the periodic table grouped by the type of atomic orbital receiving the outermost electrons. Competing predictions place superheavy elements in unfamiliar orbital blocks.
Ununpentium: The former temporary systematic name for element 115, now officially named moscovium. It shows the naming path that untriseptium would follow if element 137 were discovered.
Supercritical atom: A theoretical atom whose nuclear charge is high enough to drive a bound electron state into the negative-energy continuum. Element 137 is discussed near the point where this strong-field phenomenon may arise.
Periodic table: A tabular arrangement of chemical elements ordered by atomic number and recurring chemical properties. Element 137 would extend the table beyond all confirmed elements.
Superheavy element: A chemical element with an atomic number greater than that of the actinides, generally produced artificially and highly unstable. Element 137 would lie far beyond the confirmed superheavy elements.