Seaborgium (Sg). Diagram of the nuclear composition and electron configuration of an atom of seaborgium-269 (atomic number: 106), the most stable isotope of this radioactive element. The nucleus consists of 106 protons (red) and 163 neutrons (yellow). 106 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Seaborgium, named after Glenn Seaborg and first synthesised in 1974, is a transactinide and transition metal in group 6, period 7, and the d-block of the periodic table. Seaborgium-269 has a half-life of 2.1 minutes, its nucleus emitting an alpha particle to form rutherfordium-265.