Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 by the Norwegian mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius and named after Thor, the Norse god of thunder.Symbol: Th
Electron configuration: Rn 6d2 7s2
Atomic number: 90
Melting point: 1,755 °C
Discovered: 1828
Atomic mass: 232.03806 ± 0.00002 u