The chemical symbol for radium is Ra. It is written with a capital R followed by a lowercase a, following the standard conventions for chemical symbols.
Radium is element 88 and belongs to the alkaline earth metals in group 2 of the periodic table. Marie and Pierre Curie discovered it in 1898 while studying radioactive minerals. The name comes from the Latin radius, meaning “ray,” referring to the element’s intense radioactivity.
The most stable naturally occurring isotope, radium-226, has a half-life of about 1,600 years. As radium decays, it produces radon and other radioactive elements. Its radiation once made radium popular in luminous paints and questionable medical products, but its hazards are now well established.
The symbols Ro, Rm and Rd are not the current symbol for radium. Radium’s atomic number, 88, is also easy to confuse with polonium’s 84, another radioactive element associated with the Curies.