Radium is a chemical element with symbol Ra and atomic number 88. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226, which has a half-life of 1601 years and decays into radon gas. Because of such instability, radium is luminescent, glowing a faint blue.Symbol: Ra
Electron configuration: Rn 7s2
Discovered: 1898
Atomic number: 88
Atomic mass: 226 u
Discoverers: Pierre Curie, Marie Curie