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Mendelevium (Md). Diagram of the nuclear composition and electron configuration of an atom of mendelevium-258 (atomic number: 101), this element's most stable isotope. The nucleus consists of 101 protons (red) and 157 neutrons (blue). Mendelevium, named after Mendeleyev and first synthesised in 1955, 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 mendelevium-258 (half-life: 51 days) forms fermium-258 by electron capture.
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