090Actinide · Group 3 · Period 7
Thorium
Thorium (Th) is element 90, a actinide in the f-block — group 3, period 7. It is a solid at room temperature with 7 electron shells (2, 8, 18, 32, 18, 10, 2) and an atomic mass of 232.03774 u.
- Atomic mass
- 232.0 u
- Phase · STP
- solid
- Melting
- 2023 K · 1750 °C
- Boiling
- 5061 K · 4788 °C
- Electronegativity
- 1.3
- Density
- 11.724 g/cm³
Photograph — W. Oelen, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Identity
- Atomic number
- 90
- Standard atomic weight
- 232.0 u
- Category
- Actinide
- Group
- 3
- Period
- 7
- Block
- f-block
- Oxidation states
- +4
Physical properties
- Melting point
- 2023 K · 1750 °C
- Boiling point
- 5061 K · 4788 °C
- Density
- 11.724 g/cm³
- Molar heat capacity
- 26.23 J/(mol·K)
- Atomic radius
- 237 pm
- Electron affinity
- 112.72 kJ/mol
Atomic structure
90protons
142neutrons
90electrons
2valence e⁻
- Noble-gas notation
- [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
Periodic trends
Where Thorium ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
5871
1.1k2
1.9k3
2.8k4
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1828
- Discovered by
- Jöns Jakob Berzelius
- Named by
- —
- Appearance
- silvery, often with black tarnish