90232.04ThThorium
Thorium (Th) — element 90actinide · period 7
Thorium is a chemical element with the symbol Th and atomic number 90. It is an actinide in period 7 of the periodic table (the f-block), with a standard atomic mass of 232.04 u. At room temperature (25 °C) thorium is a solid.
💡 Known for: A weakly radioactive metal once used in gas lantern mantles and studied as a future nuclear fuel.
# Thorium properties
| Symbol | Th |
|---|---|
| Atomic number | 90 |
| Atomic mass | 232.04 u |
| Category | actinide |
| Group | — (f-block, no group number) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 6d² 7s² |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d² 7s² |
| Electrons per shell | 2, 8, 18, 32, 18, 10, 2 |
| Protons / electrons | 90 / 90 |
| State at 25 °C | solid |
| Melting point | 2115 K (1841.8 °C, 3347.3 °F) |
| Boiling point | 5061 K (4787.9 °C, 8650.1 °F) |
| Density | 11.72 g/cm³ |
| Electronegativity (Pauling) | 1.3 |
| First ionization energy | 6.307 eV |
| Atomic radius | 180 pm |
| Discovered | 1829 |
# Electron configuration of thorium
The electron configuration of thorium is [Rn] 6d² 7s², written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d² 7s². Its 90 electrons fill 7 shells as 2, 8, 18, 32, 18, 10, 2, so the outermost shell holds 2 electrons.
# Related elements
AcActiniumprevious elementPaProtactiniumnext elementUUraniumactinideNpNeptuniumactinidePuPlutoniumactinideAmAmericiumactinideCmCuriumactinideBkBerkeliumactinideCfCaliforniumactinideEsEinsteiniumactinide
# Thorium FAQ
What is the atomic number of thorium?
The atomic number of thorium is 90: every thorium atom has 90 protons in its nucleus. Its symbol is Th.
What is the atomic mass of thorium?
The standard atomic mass of thorium is 232.04 u.
What is the electron configuration of thorium?
Thorium's electron configuration is [Rn] 6d² 7s² (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d² 7s²), with 2, 8, 18, 32, 18, 10, 2 electrons per shell.
Is thorium a metal?
Yes. Thorium is an actinide, one of the metals.
What is the melting point of thorium?
Thorium melts at 2115 K (1841.8 °C, 3347.3 °F) and boils at 5061 K (4787.9 °C, 8650.1 °F).
What is thorium used for / known for?
A weakly radioactive metal once used in gas lantern mantles and studied as a future nuclear fuel.