Thorium is a radioactive metal found in minerals including monazite. Its compounds have served in catalysts and specialized optical glass, and thorium has been investigated in nuclear-energy systems. Unlike many neighbouring radioactive elements, thorium has an assigned standard atomic weight in the CIAAW table.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
Why did thorium dioxide work as a historical gas-mantle material?
Thorium dioxide in gas mantles
FOLLOW THIS RELATIONSHIP
Recognize the oxide framework
The mantle was an oxide structure rather than a piece of thorium metal. The chemical form matters when explaining its response to sustained heating.
Explore the model (optional)
ThFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Optional: check your understanding
USE THE EXPLANATION
What supplied the energy for the light in the gas-mantle account?
Atomic identity, reference properties and structure models
INTERACTIVE 3D90 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Rn] 6d2 7s2. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
A mineral specimen opens another radioactive family
Jöns Jacob Berzelius identified thorium while analyzing a Norwegian that became known as thorite. He named the element after Thor, the Norse god. Its was recognized much later, in 1898, connecting an established mineral element to a rapidly developing new science. The long interval between chemical discovery and nuclear characterization shows that identifying an element does not immediately reveal every important feature of its behavior.
1829
Element identified
Berzelius reports thorium from the mineral thorite.
1898
Radioactivity recognized
Schmidt and Marie Curie independently investigate thorium radioactivity.
Thorium occurs in minerals including thorite and monazite, often alongside rare-earth elements. Natural material is dominated by thorium-232, whose produces a family of other elements. Its occurrence in a mineral does not itself make a usable fuel: mineral processing, transformations and reactor design are separate considerations.
Thorium chemistry strongly favors the +4 , and thorium dioxide is a refractory solid. The electronic behavior of its compounds differs from the nuclear behavior that motivates fuel-cycle research. Natural thorium is fertile rather than directly fissile in the usual fuel-cycle sense: its possible energy role involves conversion to another isotope.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
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Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
solid
293.15 K, 101.325 kPa
Melting point in K
2115 K
at standard pressure unless noted
Boiling point in K
5061 K
101.325 kPa
Density in g/cm³
11.72 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
1.3 Pauling
Pauling scale
First ionization energy in kJ/mol
587 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
206 pm
single-bond covalent radius
Common oxidation states
+4
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust in mg/kg
9.6 mg/kg
upper continental crust, mass fraction
Has stable isotopes
Yesderived
Discovery year in CE
1829 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 7
Th 1.3 Pauling · Thorium
Electronegativity across period 7. Exact values.
Ra
0.9
Ac
1.1
Th
1.3
Pa
1.5
U
1.38
Np
1.36
Pu
1.28
Am
1.13
Cm
1.28
Bk
1.3
Cf
1.3
Es
1.3
Fm
1.3
Md
1.3
No
1.3
Lr
1.3
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
