Th
Thorium
Element 90 · Actinide
Thorium (Th)
Thorium is a weakly radioactive, silvery metal about three times more abundant than uranium. It is studied as a nuclear fuel.
- Actinide
- Period 7
- f-block series
- f-block
- solid at room temperature
- ☢ Radioactive
Key properties
- Atomic mass
- 232.038
- u
- Electron configuration
- [Rn] 6d2 7s2
- Melting point
- 1,749.9 °C
- 2,023 K
- Boiling point
- 4,787.9 °C
- 5,061 K
- Density
- 11.72 g/cm³
- Electronegativity
- 1.3
- Pauling
- Atomic radius
- 237 pm
- van der Waals
- 1st ionisation energy
- 6.08 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about thorium
- 01
Thorium-232 has a half-life of 14 billion years — longer than the age of the universe.
- 02
Gas lantern mantles once glowed brightly thanks to thorium oxide.
- 03
India is developing reactors to use its large thorium reserves.
Applications
What is thorium used for?
- Nuclear fuel research
- Gas lantern mantles (historically)
- Welding electrodes
- High-quality camera lenses (historically)
History
Discovery & name origin
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 90
- Atomic mass
- 232.038 u
- Group
- Actinides (3)
- Period
- 7
- Block
- f-block
- Electron configuration
- [Rn] 6d2 7s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d2
- Electrons per shell
- 2, 8, 18, 32, 18, 10, 2
- Electronegativity (Pauling)
- 1.3
- Electron affinity
- —
- Atomic radius (van der Waals)
- 237 pm
- Stable isotopes
- None — all isotopes are radioactive
Oxidation states
Highlighted: common oxidation states (+4).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st587
- 2nd1,110
- 3rd1,930
- 4th2,780
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Solid
- Melting point
- 2,023 K · 1,749.9 °C · 3,181.7 °F
- Boiling point
- 5,061 K · 4,787.9 °C · 8,650.1 °F
- Density
- 11.72 g/cm³
- Molar heat capacity
- 26.23 J/(mol·K)
- Appearance
- Silvery, often with black tarnish
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Thorium questions
What is Th on the periodic table?
Th is the symbol for thorium, element 90 on the periodic table. It sits in period 7, in the f-block, in the actinide category, and has an atomic mass of 232.038.
What is the atomic number of thorium?
Thorium has atomic number 90, so every thorium atom has 90 protons in its nucleus. Its symbol is Th and its atomic mass is 232.038.
Who discovered thorium?
Thorium was discovered by Jöns Jacob Berzelius in 1829 (Sweden). The name comes from from Thor, the Norse god of thunder.
What is thorium used for?
Thorium is used for: nuclear fuel research; gas lantern mantles (historically); welding electrodes; high-quality camera lenses (historically).
Is thorium a metal?
Yes. Thorium is a actinide, one of the metallic elements.
What is the electron configuration of thorium?
The electron configuration of thorium is [Rn] 6d2 7s2. Its 90 electrons are arranged in shells as 2, 8, 18, 32, 18, 10, 2.