Thorium (Th)
Thorium is element 90, a actinide in period 7 of the periodic table. At room temperature it is a solid.
Electron configuration [Rn] 6d2 7s2
Electrons per shell 2, 8, 18, 32, 18, 10, 2
Thorium data
| Atomic number | 90 |
|---|---|
| Symbol | Th |
| Atomic mass | 232.038 u |
| Category | Actinide |
| Group | — (f-block) |
| Period | 7 |
| Block | f |
| State at 25 °C | solid |
| Melting point | 2023 K (1749.9 °C) |
| Boiling point | 5093 K (4819.9 °C) |
| Density | 11.724 g/cm³ |
| Electronegativity (Pauling) | 1.3 |
| Atomic radius | — |
| 1st ionization energy | 587 kJ/mol |
| Electron affinity | — |
| Oxidation states | +2, +3, +4 |
| Common ion charge | 4+ |
| Discovered | 1828 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through thorium’s configuration and its ions →
Where thorium sits
Thorium belongs to the actinides. Its Pauling electronegativity of 1.3 is mid-range; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Thorium FAQ
What is the electron configuration of thorium?
Thorium (Z = 90) has the configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p6 6d2 7s2. In noble-gas shorthand that is [Rn] 6d2 7s2. This is an exception to the simple Aufbau prediction (1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f2 6s2 6p6 7s2); a half-filled or filled subshell lowers the energy.
How many valence electrons does thorium have?
4 (2 outer s + 2 d electrons; 2 in the outermost shell).
What is the atomic mass of thorium?
The standard atomic weight of thorium is 232.038 u, so one mole weighs 232.038 g.
Is thorium a metal?
Yes. Thorium is a actinide.
What is the charge of a thorium ion?
Thorium most commonly forms Th4+.