Ununoctium (Uuo). Diagram of the nuclear composition and electron configuration of an atom of ununoctium-294 (atomic number: 118), the only known isotope of this radioactive element. The nucleus consists of 118 protons (red) and 176 neutrons (yellow). 118 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Ununoctium is a temporary name (2002 synthesis not yet official). It is a transactinide of unknown properties in group 18, period 7, and the p-block of the periodic table. The ununoctium-294 nucleus (half-life: 0.89 milliseconds) emits an alpha particle to form ununhexium-290.