Radium is hot stuff! It was used in self-luminating paints on alarm clocks and other devices into the 1950s, when it fell out of use due to the radioactive impacts on the paint process employees. Its chemical symbol is Ra and its atomic number 88. This means it has 88 electrons 88 protons. Check out this video of a fantastic thrift store find!
The famous Madam Currie discovered radium in 1898.
Read a very interesting retrospective from the Atlantic Monthly on this once alluring but very dangerous element.