Curium (Cm). Diagram of the nuclear composition and electron configuration of an atom of curium-247 (atomic number: 96), an isotope of this element. The nucleus consists of 96 protons (red) and 151 neutrons (yellow). 96 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Curium, named after the Curies and first synthesised in 1944, is an actinide and transuranic element in period 7, and the f-block of the periodic table. Actinides are soft radioactive metals. The nucleus of curium-248 (half-life: 348,000 years) emits an alpha particle to form plutonium-244.