Element 90 · Actinide
Thorium (Th) — Element 90
Thor, Norse god
Thorium (Th) is an actinide in Period 7 (f-block) of the periodic table with atomic number 90, standard atomic weight 232.04 u, and ground-state electron configuration [Rn] 6d² 7s². At standard temperature and pressure it is classified as a solid with 4 valence electrons and common oxidation states +4.
Nuclear fuel research, optics
What are the atomic properties and physical constants of Thorium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 90
- Standard atomic mass
- 232.04 u
- Chemical family
- Actinide
- Ground-state configuration
- [Rn] 6d² 7s²
- Electrons per shell
- 2, 8, 18, 32, 18, 10, 2
- Valence electrons
- 4
- Common ion charges / oxidation states
- +4
- Phase at STP
- Solid
- Pauling electronegativity
- 1.30 Pauling
- First ionization energy
- 587 kJ/mol
- Atomic radius
- —
- Melting point
- 1,750 °C
- Boiling point
- 4,788 °C
- Discovery year
- 1829
- Table coordinate
- Period 7, f-block
- Radioactivity
- Radioactive (no stable isotopes)
How are electrons arranged across Thorium’s shells?
A neutral Thorium atom contains 90 electrons distributed across 7 occupied principal energy shells ([Rn] 6d² 7s²). The table below compares Thorium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Th | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 32 e⁻ | 32 e⁻ |
| n = 5 | O | 18 e⁻ | 50 e⁻ |
| n = 6 | P | 10 e⁻ | 72 e⁻ |
| n = 7 | Q | 2 e⁻ | 98 e⁻ |
Frequently Asked Questions about Thorium (Th)
What is the atomic mass and atomic number of Thorium (Th)?
Thorium (Th) has atomic number Z = 90 (90 protons in its nucleus) and an IUPAC standard atomic weight of 232.04 u. It sits in Period 7 in the f-block and is classified as an actinide.
What is the ground-state electron configuration of Thorium?
The neutral ground-state electron configuration of Thorium (Z = 90) is [Rn] 6d² 7s². Across its 7 occupied principal shells (n = 1 to n = 7), the electrons per shell are 2, 8, 18, 32, 18, 10, 2, with 4 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Thorium?
Thorium commonly forms +4 oxidation states or ion charges in compounds. Its Pauling electronegativity is 1.30 and its first ionization energy is 587 kJ/mol.
When was Thorium discovered and what is it used for?
Thorium was discovered in 1829 (Thor, Norse god). Nuclear fuel research, optics
How does Thorium compare to neighboring elements?
Other actinide elements: