Thorium
Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only two significantly radioactive elements that still occur naturally in large quantities as a primordial element (the other being uranium). It was discovered in 1828 by the Norwegian Reverend and amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius, who named it after Thor, the Norse god of thunder.
A stylized shell model. Electrons are quantum objects, not particles following these literal paths. Sizes and motion are illustrative.
86 is the [Rn] core total across six shells.
At a glance
- Atomic number
- 90
- Atomic mass
- 232.03774 u
- Phase
- Solid
- Density
- 11.724 g/cm³
- Melting point
- 2,023 K
- Boiling point
- 5,061 K
- First ionization energy
- 587 kJ/mol
- Electronegativity
- 1.3
- Electron affinity
- 112.72 kJ/mol
- Molar heat capacity
- 26.23 J/(mol·K)
- Period
- 7
- Appearance
- silvery, often with black tarnish
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.