Radium (Ra) was discovered in the ore pitchblende by the French chemists Marie and Pierre Curie and an assistant in 1898. It is a radioactive element, classified as an alkaline earth metal in the periodic table. It is found naturally in uranium and thorium ores, and when isolated, it is a slivery, lustrous, and soft metal. Radium is formed by the radioactive disintegration of uranium. Radiation from radium harms living cells, and overexposure to its rays can burn. Because cancer cells are more sensitive to radiation than normal cells, radium is used in the treatment of a few types of cancer. Radium was once used in the production of luminous paints that were applied to clock dials and other objects to make them glow in the dark, until its harmful effects became widely known. This book gives readers a comprehensive overview of the properties and uses of the radioactive element radium and its place on the periodic table.