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Ununpentium (Uup). Diagram of the nuclear composition and electron configuration of an atom of ununpentium-288 (atomic number: 115), the most stable isotope of this radioactive element. The nucleus consists of 115 protons (red) and 173 neutrons (blue). Ununpentium is a temporary name (2003 synthesis not yet official). It is a transactinide of unknown properties in group 15, period 7, and the p-block of the periodic table. The ununpentium-288 nucleus (half-life: 173 milliseconds) emits an alpha particle to form ununtrium-284.
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