Ununennium
Ununennium, also known as eka-francium or element 119, is a hypothetical chemical element; it has symbol Uue and atomic number 119. Ununennium and Uue are the temporary systematic IUPAC name and symbol respectively, which are used until the element has been discovered, confirmed, and a permanent name is decided upon. In the periodic table of the elements, it is expected to be an s-block element, an alkali metal, and the first element in the eighth period. It is the lightest element that has not yet been synthesized.
| Theoretical element | ||||||
|---|---|---|---|---|---|---|
| Ununennium | ||||||
| Pronunciation | /ˌuːn.uːnˈɛniəm/ ⓘ | |||||
| Alternative names | element 119, eka-francium | |||||
| Ununennium in the periodic table | ||||||
| ||||||
| Atomic number (Z) | 119 | |||||
| Group | group 1: hydrogen and alkali metals | |||||
| Period | period 8 (theoretical, extended table) | |||||
| Block | s-block | |||||
| Electron configuration | [Og] 8s1 (predicted) | |||||
| Electrons per shell | 2, 8, 18, 32, 32, 18, 8, 1 (predicted) | |||||
| Physical properties | ||||||
| Phase at STP | unknown phase (could be solid or liquid) | |||||
| Melting point | 273–303 K (0–30 °C, 32–86 °F) (predicted) | |||||
| Boiling point | 903 K (630 °C, 1166 °F) (predicted) | |||||
| Density (near r.t.) | 3 g/cm3 (predicted) | |||||
| Heat of fusion | 2.01–2.05 kJ/mol (extrapolated) | |||||
| Atomic properties | ||||||
| Oxidation states | (+1), (+3), (+5) (predicted) | |||||
| Electronegativity | Pauling scale: 0.86 (predicted) | |||||
| Ionization energies |
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| Atomic radius | empirical: 240 pm (predicted) | |||||
| Covalent radius | 263–281 pm (extrapolated) | |||||
| Other properties | ||||||
| Crystal structure | body-centered cubic (bcc) (extrapolated) | |||||
| CAS Number | 54846-86-5 | |||||
| History | ||||||
| Naming | IUPAC systematic element name | |||||
| Isotopes of ununennium | ||||||
| Experiments and theoretical calculations | ||||||
An attempt to synthesize the element has been ongoing since 2018 in RIKEN in Japan. The Joint Institute for Nuclear Research in Dubna, Russia, plans to make an attempt at some point in the future, but a precise date has not been released to the public. Theoretical and experimental evidence has shown that the synthesis of ununennium will likely be far more difficult than that of the previous elements.
Ununennium's position as the seventh alkali metal suggests that it would have similar properties to its lighter congeners. However, relativistic effects may cause some of its properties to differ from those expected from a straight application of periodic trends. For example, ununennium is expected to be less reactive than caesium and francium and closer in behavior to potassium or rubidium, and while it should show the characteristic +1 oxidation state of the alkali metals, it is also predicted to show the +3 and +5 oxidation states, which are unknown in any other alkali metal.