Thorium: the essentials
- Name: thorium
- Symbol: Th
- Atomic number: 90
- Relative atomic mass (Ar): 232.0377 (4) [see note g]
- Standard state: solid at 298 K
- Appearance: silvery white
- Classification: Metallic
- Group in periodic table:
- Group name: Actinoid
- Period in periodic table: 7 (actinoid)
- Block in periodic table: f
- Shell structure: 188.8.131.52.18.10.2
- CAS Registry: 7440-29-1
Thorium atoms have 90 electrons and the shell structure is 184.108.40.206.18.10.2. The ground state electronic configuration of neutral thorium is [Rn].6d2.7s2 and the term symbol of thorium is 3F2.
Thorium is a source of nuclear power. There is probably more untapped energy available for use from thorium in the minerals of the earth's crust than from combined uranium and fossil fuel sources. Much of the internal heat the earth has been attributed to thorium and uranium.
When pure, thorium is a silvery white metal which is air-stable and retains its lustre for several months. When contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and finally black. Thorium oxide has a melting point of 3300°C, the highest of all oxides. Only a few elements, such as tungsten, and a few compounds, such as tantalum carbide, have higher melting points.
Thorium is slowly attacked by water, but does not dissolve readily in most common acids, except hydrochloric. Powdered thorium metal is often pyrophoric and should be carefully handled.When heated in air, thorium turnings ignite and burn brilliantly with a white light.
Thorium is named for Thor, the Scandinavian god of war. It is found in thorite and thorianite in New England (USA) and other sites.
Image adapted with permission from Prof James Marshall's (U. North Texas, USA) Walking Tour of the elements CD.
Thorium: physical properties
- Density of solid: 11724 kg m-3
- Molar volume: 19.80 cm3
- Thermal conductivity: 54 W m‑1 K‑1
Thorium: heat properties
- Melting point: 2115 [1750 °C (3182 °F)] K
- Boiling point: 5093 [4820 °C (8708 °F)] K
- Enthalpy of fusion: 20.5 kJ mol-1
Thorium: atom sizes
- Atomic radius (empirical): 180 pm
- Molecular single bond covalent radius: 175 (coordination number 4) ppm
- van der Waals radius: [ 305 ] ppm
- Pauling electronegativity: 1.3 (Pauling units)
- Allred Rochow electronegativity: 1.11 (Pauling units)
- Mulliken-Jaffe electronegativity: (no data)
Thorium: orbital properties
- First ionisation energy: 608.50 kJ mol‑1
- Second ionisation energy: 1167 kJ mol‑1
- Third ionisation energy: 1768 kJ mol‑1
- Universe: 0.4 ppb by weight
- Crustal rocks: 6000 ppb by weight
- Human: (no data) ppb by weight
Thorium: crystal structure
Thorium: biological data
- Human abundance by weight: (no data) ppb by weight
Thorium has no biological role.
Reactions of thorium as the element with air, water, halogens, acids, and bases where known.
Thorium: binary compounds
Binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and other compounds of thorium where known.
Thorium: compound properties
Bond strengths; lattice energies of thorium halides, hydrides, oxides (where known); and reduction potentials where known.
Thorium: historyThorium was discovered by Jöns Berzelius in 1829 at Sweden. Origin of name: named after "Thor", the mythological Scandinavian god of war.
Isolation: coming soon!