Ununennium - WikiHQ

Ununennium, also known

: + → * → no atoms

More practical production of further superheavy elements requires projectiles heavier than Ca, but this makes the reaction more symmetric

From April to September 2012, an attempt to synthesize Uue and Uue was made by bombarding a target of berkelium-249 with titanium-50 at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. This reaction between Bk and Ti was predicted to be the most favorable practical reaction for formation of ununennium, Due to the predicted short half-lives, the GSI team used new "fast" electronics capable of registering decay events within microseconds. The experiment was originally planned to continue to November 2012, but was stopped early to make use of the Bk target to confirm the synthesis of tennessine (thus changing the projectile to Ca). The Cm targets were provided by Oak Ridge National Laboratory. RIKEN developed a high-intensity vanadium beam. The experiment began at a cyclotron while RIKEN upgraded its linear accelerators; the upgrade was completed in 2020. Bombardment may be continued with both machines until the first event is observed.

: + → * → no atoms yet

The produced isotopes of ununennium are expected to undergo two alpha decays to known isotopes of moscovium, Mc and Mc. This would anchor them to a known sequence of five or six further alpha decays, respectively, and corroborate their production.

As of September 2023, the team at RIKEN had run the Cm+V reaction for 462 days. A report by the RIKEN Nishina Center Advisory Committee noted that this reaction was chosen because of the availability of the target and projectile materials, despite predictions favoring the Bk+Ti reaction, because the Ti projectile is closer to doubly magic Ca and has an even atomic number (22); reactions with even-Z projectiles have generally been shown to have greater cross-sections. As of August 2024, the team at RIKEN was still running this reaction "24/7".

Planned

The team at the JINR plans to attempt synthesis of element 119. In late 2023, the JINR reported the first successful synthesis of a superheavy element with a projectile heavier than Ca: U was bombarded with Cr to make a new isotope of livermorium (element 116), Lv. Successful synthesis of a superheavy nuclide in this experiment was an unexpectedly good result; the aim was to experimentally determine the cross-section of a reaction with Cr projectiles and prepare for the synthesis of element 120. The JINR has also alluded to a future attempt to synthesize element 119 with the same projectile, bombarding Am with Cr. In February 2026, Yuri Oganessian at the JINR stated that an experiment to synthesize element 119 should begin in May of that year. The team at the Heavy Ion Research Facility in Lanzhou (HIRFL), which is operated by the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences, also plans to try the Am+Cr reaction.

Naming

Using Mendeleev's nomenclature for unnamed and undiscovered elements, ununennium should be known as eka-francium. Using the 1979 IUPAC recommendations, the element should be temporarily called ununennium (symbol Uue) until it is discovered, the discovery is confirmed, and a permanent name chosen. Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations are mostly ignored among scientists who work theoretically or experimentally on superheavy elements, who call it "element 119", with the symbol E119, (119) or 119.]]

The stability of nuclei decreases greatly with the increase in atomic number after curium, element 96, whose half-life is four orders of magnitude longer than that of any currently known higher-numbered element. All isotopes with an atomic number above 101 undergo radioactive decay with half-lives of less than 30 hours. No elements with atomic numbers above 82 (after lead) have stable isotopes. Nevertheless, for reasons not yet well understood, there is a slight increase of nuclear stability around atomic numbers 110–114, which leads to the appearance of what is known in nuclear physics as the "island of stability". This concept, proposed by University of California professor Glenn Seaborg, explains why superheavy elements last longer than predicted.

The alpha-decay half-lives predicted for 291–307Uue are on the order of microseconds. The longest alpha-decay half-life predicted is ~485 microseconds for the isotope 294Uue. When factoring in all decay modes, the predicted half-lives drop further to only tens of microseconds.

Atomic and physical

Being the first period 8 element, ununennium is predicted to be an alkali metal, taking its place in the periodic table below lithium, sodium, potassium, rubidium, caesium, and francium. Each of these elements has one valence electron in the outermost s-orbital (valence electron configuration ns1), which is easily lost in chemical reactions to form the +1 oxidation state: thus, the alkali metals are very reactive elements. Ununennium is predicted to continue the trend and have a valence electron configuration of 8s1. It is therefore expected to behave much like its lighter congeners; however, it is also predicted to differ from the lighter alkali metals in some properties. The effect is called subshell splitting, as it splits the 7p subshell into more-stabilized and the less-stabilized parts. Computational chemists understand the split as a change of the second (azimuthal) quantum number ℓ from 1 to and for the more-stabilized and less-stabilized parts of the 7p subshell, respectively.]]

Due to the stabilization of its outer 8s electron, ununennium's first ionization energy—the energy required to remove an electron from a neutral atom—is predicted to be 4.53 eV, higher than those of the known alkali metals from potassium onward. This effect is so large that unbiunium (element 121) is predicted to have a lower ionization energy of 4.45 eV, so that the alkali metal in period 8 would not have the lowest ionization energy in the period, as is true for all previous periods. Indeed, the static dipole polarisability (αD) of ununennium, a quantity for which the impacts of relativity are proportional to the square of the element's atomic number, has been calculated to be small and similar to that of sodium.

The electron of the hydrogen-like ununennium atom—oxidized so it has only one electron, Uue118+—is predicted to move so quickly that its mass is 1.99 times that of a non-moving electron, a consequence of relativistic effects. For comparison, the figure for hydrogen-like francium is 1.29 and the figure for hydrogen-like caesium is 1.091. The boiling point of ununennium is expected to be around 630 °C, similar to that of francium, estimated to be around 620 °C; this is lower than caesium's boiling point of 671 °C. or rubidium in addition to the +1 oxidation state that is characteristic of the other alkali metals and is also the main oxidation state of all the known alkali metals: this is because of the destabilization and expansion of the 7p spinor, causing its outermost electrons to have a lower ionization energy than what would otherwise be expected. Thus, instead of ununennium being the most electropositive element, as a simple extrapolation would seem to indicate, caesium retains this position, with ununennium's electronegativity most likely being close to sodium's (0.93 on the Pauling scale). From these M dissociation energies, the enthalpy of sublimation (ΔH) of ununennium is predicted to be 94 kJ/mol (the value for francium should be around 77 kJ/mol). The Uue–Au bond should be the weakest of all bonds between gold and an alkali metal, but should still be stable. This gives extrapolated medium-sized adsorption enthalpies (−ΔH) of 106 kJ/mol on gold (the francium value should be 136 kJ/mol), 76 kJ/mol on platinum, and 63 kJ/mol on silver, the smallest of all the alkali metals, that demonstrate that it would be feasible to study the chromatographic adsorption of ununennium onto surfaces made of noble metals.