Ununtrium (Uut). Diagram of the nuclear composition and electron configuration of an atom of ununtrium-286 (atomic number: 113), the most stable isotope of this radioactive element. The nucleus consists of 113 protons (red) and 173 neutrons (yellow). 113 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Ununtrium is a temporary name (2003 synthesis not yet official). It is a transactinide of unknown properties in group 13, period 7, and the p-block of the periodic table. The ununtrium-286 nucleus (half-life: 19.6 seconds) emits an alpha particle to form roentgenium-282.