Atomic Number 91     Mass of Most Important Isotope 231.03588

Density 15.37 g/mL     State solid     Color metallic    

Electronegativity 1.38     No Natural Isotopes

Abbreviated Electron Configuration [Rn] 5f³ 6s²

Discovered by Otto Hahn, Lise Meitner, John Cranston, and Friedrich Soddy in 1917.