Thorium (Th)
Actinide · Radioactive
Thorium is a mildly radioactive metal named after the thunder god Thor. More abundant than uranium, it has long been touted as an alternative nuclear fuel, and it once lit millions of homes in glowing gas-lamp mantles.
Position on the periodic table
Atomic properties
| Atomic number | 90 |
|---|---|
| Atomic mass | 232.038 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d2 |
| Noble gas shorthand | [Rn] 6d2 7s2 |
| Electrons per shell | 2, 8, 18, 32, 18, 10, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +4 |
| Electronegativity (Pauling) | 1.3 |
| Covalent radius (approx.) | 206 pm |
| First ionization energy | 587 kJ/mol |
| Electron affinity | 112.7 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 11.72 g/cm³ |
| Melting point | 1749.8 °C (2023 K) |
| Boiling point | 4787.9 °C (5061 K) |
| Appearance | silvery, often with black tarnish |
| Radioactive | Yes |
| Origin | Occurs naturally |
Electron configuration of thorium
Thorium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d2, usually shortened to [Rn] 6d2 7s2. Its electrons occupy 7 shells (2, 8, 18, 32, 18, 10, 2), placing it in period 7 of the f-block. Explore it interactively in the electron configuration calculator.
Uses of thorium
- Potential nuclear fuel (thorium fuel cycle research)
- High-temperature ceramics and crucibles
- Historic gas-lamp mantles and camera lenses
- Magnesium alloys for aerospace
Biological role: None.
Occurrence: About three times more abundant than uranium; mined from monazite sands.
Common compounds of thorium
ThO2
Thorium dioxide
History and discovery
Discovered: 1829 — Jöns Jakob Berzelius. Name origin: Named after Thor, the Norse god of thunder.
Jöns Jacob Berzelius identified thorium in 1829; its radioactivity was recognised by Gerhard Schmidt and Marie Curie in 1898.
Safety notes
Radioactive with an extremely long half-life; the main hazard is inhaled dust.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Thorium
1. What is the chemical symbol of Thorium?
2. What is the atomic number of Thorium?
3. Which category does Thorium belong to?
4. What is the state of Thorium at room temperature?
5. Which period of the periodic table is Thorium in?
Thorium FAQs
What is the atomic number of thorium?
Thorium's atomic number is 90 — every thorium atom has 90 protons in its nucleus.
What is the symbol for thorium?
Th. Named after Thor, the Norse god of thunder.
Is thorium a metal, nonmetal, or metalloid?
Thorium is classified as a actinide.
What state is thorium at room temperature?
At about 25 °C, thorium is a solid. It melts at 1749.8 °C.
What is thorium used for?
Key uses include: potential nuclear fuel (thorium fuel cycle research); high-temperature ceramics and crucibles; historic gas-lamp mantles and camera lenses.
Related elements
Keep working with this element
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