Ununennium, temporarily designated as element 119 with the systematic symbol Uue, is the provisional name for the first chemical element beyond the known periodic table rows so far synthesized. As a predicted chemical element, it has not yet been created in a laboratory, and its properties are inferred from theory, trends in the periodic table, and advanced atomic models that include relativistic effects. The temporary IUPAC name ununennium literally encodes its atomic number (one-one-nine) until a confirmed discovery allows researchers to propose a permanent name and symbol.

Predicted position and electronic character

Element 119 is expected to occupy Group 1 of an extended periodic table (the alkali metal group) and to begin a new period (period 8). Simple extrapolation of periodic trends suggests it would behave somewhat like other alkali metals: a single valence electron outside a closed-shell core. However, for such heavy nuclei, relativistic effects on the innermost electrons become pronounced and can alter orbital energies and chemical behavior. Many theoretical studies therefore predict deviations from classical alkali-metal behavior — for example, modified ionization energies, unusual oxidation states, or weaker metallic character than lighter congeners.

Isotopes and nuclear stability

All isotopes of ununennium are expected to be radioactive. Predicted nuclides would have very short half-lives in most cases, decaying by alpha emission, spontaneous fission, or other modes typical for superheavy nuclei. Nuclear models also discuss the possibility of an "island of stability" at higher proton and neutron numbers, where particular combinations might yield longer-lived isotopes; whether any isotope of element 119 lies close enough to that region to have appreciable stability remains uncertain. For general information on nuclear species, see isotopes.

Synthesis methods and experimental challenges

Efforts to produce element 119 rely on heavy-ion fusion reactions carried out at accelerator facilities. In these experiments, a heavy actinide target is bombarded with a lighter projectile beam at very high energy in the hope that the two nuclei fuse and evaporate a small number of neutrons to form the desired superheavy nucleus. Such experiments are difficult because cross sections (formation probabilities) fall rapidly with increasing atomic number, and the produced atoms are extremely short-lived and produced at rates of at best a few atoms per month or year. Teams in several countries have attempted or planned searches using high-intensity beams and highly purified targets; these projects require long irradiation times, sophisticated separators to isolate reaction products, and sensitive detectors to identify characteristic decay chains.

History of attempts and ongoing research

There have been multiple experimental campaigns aimed at producing element 119, conducted by groups in national laboratories with expertise in superheavy element research. Previous successes in synthesizing elements up to 118 relied on particular projectile-target combinations and very sensitive detection methods. As the community pushes to element 119 and beyond, collaborations between accelerator facilities and nuclear chemists continue to refine target materials, beam species and energies, and detector arrays. Planned and ongoing experiments remain an active part of superheavy element science.

Scientific importance and potential uses

Although any practical applications for ununennium are speculative given its expected radioactivity and likely short half-lives, the search for element 119 advances fundamental science. Synthesizing new elements tests nuclear models, refines our understanding of nuclear forces and shell structure, probes relativistic quantum chemistry, and helps map the limits of the periodic table. Results feed into theoretical work that may predict the location of more stable superheavy nuclides and inform future experiments. For context on chemical classification, see alkali metal.

  • Temporary name: ununennium (symbol Uue) under the IUPAC systematic naming system.
  • Atomic number: 119 — the next element after oganesson (118).
  • Expected chemistry: Group 1 analog with possible relativistic departures from simple trends.
  • Production: attempted via heavy-ion fusion in accelerator facilities; no confirmed synthesis to date.

Discovery of element 119 will require reproducible experimental evidence and peer-reviewed confirmation. Until then, ununennium remains a focus of theoretical prediction and experimental ambition, illustrating both the challenges and rewards of exploring the heaviest reaches of the periodic table.