What element has atomic number 88?

The element with atomic number 88 is radium.

Atomic number counts the protons in an atom’s nucleus, so every radium atom has 88 protons. Radium’s chemical symbol is Ra, and it belongs to group 2 of the periodic table, the alkaline earth metals. It sits below barium and above radium’s position in the period-7 sequence, with actinium following it.

Marie and Pierre Curie discovered radium in 1898 while examining pitchblende, a uranium-rich mineral. They noticed that the ore was far more radioactive than its uranium content could explain. After painstaking chemical separation, they identified radium chloride and named the element from the Latin word radius, meaning “ray.” Marie Curie isolated radium metal in 1910.

Radium has no stable isotopes. Radium-226, its most stable naturally occurring isotope, has a half-life of about 1,600 years and decays to radon. Early radium paints famously glowed in the dark, but the element is highly radioactive, toxic, and carcinogenic.