The element with atomic number 119, known provisionally as Ununennium, has not yet been officially discovered or confirmed. It is the lightest element on the periodic table that scientists have not yet successfully synthesized. For a new element to be recognized, the International Union of Pure and Applied Chemistry (IUPAC) must confirm its creation based on repeatable, verifiable evidence. The search for this element represents the current frontier in the quest for superheavy elements, pushing the limits of nuclear physics and accelerator technology.
Nomenclature and Place on the Periodic Table
Ununennium (Uue) is the temporary, systematic name designated by IUPAC for the element with the atomic number 119. This nomenclature is based on the Latin roots for the atomic number (one-one-nine), followed by the elemental suffix -ium. Historically, the element is also known as eka-francium, following Dmitri Mendeleev’s tradition of predicting unknown elements based on their lighter congener in the same group.
Element 119 is predicted to be the first element in the eighth period of the periodic table, positioning it directly below francium (Fr) in Group 1, making it the seventh alkali metal. Scientists expect its outermost electron configuration to follow the pattern of the alkali metals, possessing a single electron in the 8s orbital. Although it should exhibit the characteristic +1 oxidation state, theoretical models suggest it would be less reactive than francium and cesium. This deviation from typical periodic trends is due to relativistic effects, where the high speed of electrons in heavy nuclei alters their energy levels and chemical behavior.
The First Search Attempt
The first documented attempt to synthesize element 119 occurred in 1985 at the SuperHILAC accelerator at the Lawrence Berkeley National Laboratory in California. American researchers attempted to create the element using a heavy-ion fusion reaction. They bombarded a target of einsteinium-254 (\(^{254}\text{Es}\)) with a beam of calcium-48 (\(^{48}\text{Ca}\)) ions. The reaction aimed to merge the two nuclei, creating a compound nucleus of element 119 with an atomic mass of 302 (\(^{302}\text{Uue}\)). The experiment concluded without detecting any atoms of element 119, highlighting the difficulty of obtaining sufficient quantities of the rare and radioactive einsteinium-254 target.
The Synthesis Challenge
Element 119 remains undiscovered due to the extreme difficulty of the nuclear physics required for its creation. Scientists synthesize superheavy elements using heavy-ion fusion reactions, accelerating a lighter nucleus (the projectile) into a heavy nucleus (the target). The process requires immense precision in energy to overcome the repulsive electrical forces between the positively charged nuclei, known as the Coulomb barrier.
A major obstacle is the extremely low probability of successful fusion, quantified by the production cross-section. For Ununennium, predicted cross-sections are measured in femtobarns, meaning only a single atom might be produced after months of continuous bombardment. Furthermore, the resulting isotopes are predicted to have very short half-lives, lasting only microseconds. This short existence demands highly sensitive detection systems to register the brief decay chain before the atom vanishes.
Current Status and Future Plans
The search for Ununennium is an ongoing international effort, with major research facilities continuing to probe the limits of nuclear stability. The RIKEN laboratory in Wakō, Japan, began an attempt in January 2018, using a beam of vanadium-51 (\(^{51}\text{V}\)) to bombard a target of curium-248 (\(^{248}\text{Cm}\)). This approach utilizes a different projectile and a target that is easier to prepare than einsteinium. The Joint Institute for Nuclear Research (JINR) in Dubna, Russia, has also announced plans to attempt synthesis in the near future. If an experiment successfully synthesizes an atom of Ununennium, the discovery must be confirmed by the Joint Working Group (JWP) of IUPAC and the International Union of Pure and Applied Physics (IUPAP). Once the JWP verifies the data, the discovery team will propose a permanent name and symbol to replace the provisional name Ununennium.