Chemical element · Atomic number 90
Thorium
Thorium in the periodic table: atomic number 90, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.
Actinide
solid
232.038 u
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Atomic classification
Shell occupancy
Thorium in the Bohr shell model
This shows the electron distribution of the neutral atom in a simplified shell model.
- K · n=1
- 2 electrons
- L · n=2
- 8 electrons
- M · n=3
- 18 electrons
- N · n=4
- 32 electrons
- O · n=5
- 18 electrons
- P · n=6
- 10 electrons
- Q · n=7
- 2 electrons
- Electron configuration
- [Rn]7s2 6d2
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 10 · 2
- Group
- not reported
- Period
- 7
- Block
- F
- Element category
- Actinide
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Physical and chemical properties
- Atomic mass
- 232.038 u
- Standard state
- solid
- Density
- 11.72 g/cm³
- Melting point
- 2,023 K
- Boiling point
- 5,061 K
- Electronegativity
- 1.3 (Pauling)
- First ionisation energy
- 6.08 eV
- Oxidation states
- +4
- Discovery
- 1828
Safety and periodic classification
Safety
Safe handling cannot be inferred from Thorium's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.
Position and comparison
Thorium is in period 7 and the F block. Its direct neighbours by atomic number are Actinium and Protactinium. The recorded Pauling electronegativity is 1.3. Periodic trends are compared only through the separately sourced neighbouring values.
Sources and scope
PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.