Lawrencium (Lr). Diagram of the nuclear composition and electron configuration of an atom of lawrencium-261 (atomic number: 103), one of this element's most stable isotopes. The nucleus consists of 103 protons (red) and 158 neutrons (yellow). 103 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Lawrencium, named after Ernest Lawrence and first synthesised in 1961, is an actinide and transuranic element in group 3, period 7, and the d-block of the periodic table. Actinides are soft radioactive metals. Lawrencium-261 has a half-life of 44 minutes (3.6 hours for lawrencium-262).