Unhexennium

Unhexennium is the IUPAC systematic temporary name for hypothetical chemical element 169, with the symbol Uhe. No element with this name has been discovered or confirmed.

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IUPAC systematic element name: A temporary name formed from an element’s atomic number using standardized numerical roots and an element-name ending. Unhexennium is assembled from the roots for 1, 6, and 9 under this naming system.
Numerical roots in systematic element names: The syllables used to encode decimal digits in temporary element names: un, bi, tri, quad, pent, hex, sept, oct, and enn. The roots un, hex, and enn encode the digits of 169 in Unhexennium.
Systematic element naming: The standardized procedure for assigning temporary names and symbols to elements before their discovery is confirmed and permanent names are approved. Unhexennium follows this procedure because element 169 has not been confirmed.
Extended periodic table: Proposed arrangements of chemical elements beyond the currently confirmed periodic table. Element 169 would occupy a position in a periodic table extended far beyond known elements.
IUPAC: The International Union of Pure and Applied Chemistry, which develops international standards for chemical nomenclature and measurement. IUPAC established the rules that generate Unhexennium and its symbol.
Nuclear fusion: A nuclear reaction in which atomic nuclei combine to form a heavier nucleus. Fusion reactions are a possible route to synthesizing nuclei beyond the currently confirmed elements.
Transfermium Wars: A dispute among research groups in the 1960s and 1970s over the discovery and naming of elements 104 through 106. Earlier naming conflicts helped motivate clearer international procedures for transfermium and heavier elements.
Nuclear stability of superheavy elements: The study of how proton-neutron balance and nuclear structure determine the lifetimes of superheavy nuclei. The existence and lifetime of any element-169 isotope depend on unresolved stability limits.
Chemical element: A pure substance whose atoms all have the same number of protons in their nuclei. Element 169 would be defined by nuclei containing 169 protons.
Island of stability: A predicted region of relatively long-lived superheavy nuclei associated with particular proton and neutron numbers. Predictions about nuclear stability shape whether element 169 could persist long enough to detect.