Ununoctium is IUPAC's temporary name[11] for the transactinide element with the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is currently the only synthetic member of group 18. It has the highest atomic number and highest atomic mass of all known elements.
The radioactive ununoctium atom is very unstable, due to its high mass, and since 2005, only three or possibly four atoms of the isotope 294Uuo have been detected.[12] Although this allowed very little experimental characterization of its properties and possible compounds, theoretical calculations have resulted in many predictions, including some surprising ones. For example, although ununoctium is a member of group 18, it may possibly not be a noble gas, unlike all the other group 18 elements.[1] It was formerly thought to be a gas under normal conditions but is now predicted to be a solid due to relativistic effects.[1]
The first decay of atoms of ununoctium was observed at the Joint Institute for Nuclear Research (JINR) by Yuri Oganessian and his group in Dubna, Russia, in 2002.[19] On 9 October 2006, researchers from JINR and Lawrence Livermore National Laboratory of California, US, working at the JINR in Dubna, announced[10] that they had indirectly detected a total of three (possibly four) nuclei of ununoctium-294 (one or two in 2002[20] and two more in 2005) produced via collisions of californium-249 atoms and calcium-48 ions.[21][22][23][24][25]
- 249
98Cf + 48
20Ca → 294
118Uuo + 3 n.
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