Radium (Ra). Diagram of the nuclear composition,electron configuration,chemical data,and valence (outer electron) orbitals of an atom of radium-226 (atomic number: 88),the most stable isotope of this element. The nucleus consists of 88 protons (red) and 138 neutrons (orange). 88 electrons (white) successively occupy available electron shells (rings). Radium is a radioactive alkaline earth metal in group 2,period 7,and the s-block of the periodic table. Formed in uranium ores,the Curies discovered it in 1898. Radium-226,once used in watches,has a half-life of 1061 years,with the unstable nucleus emitting an alpha particle to form radon-222 |