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90Th232.04
Actinidessolid at STPF-block

Thorium

Group: f-block•Period: 7•Standard Atomic Weight: 232.04 u
Open Full Periodic TableView Bohr Model

Why is Thorium in this position?

Understanding the scientific rationale behind Thorium's position in the periodic table:

Group Assignment
Group Lanthanide / Actinide

Actinide series element filling the 6d/5f subshells.

Period Assignment
Period 7

Belongs to Period 7 because its outermost electrons occupy n=7.

Orbital Block
F-block

Belongs to the f-block actinide series (though ground-state configuration is [Rn] 6d² 7s²).

Chemical Category
Actinides

Classified as an actinide radioactive metal with +4 dominant chemistry.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 18, 32, 18, 10, 2]

Bohr Atomic Shell Model(2, 8, 18, 32, 18, 10, 2)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

90 Protons (p⁺)142 Neutrons (n⁰)
KShell K: Electron 1 of 2Shell K: Electron 2 of 2LShell L: Electron 1 of 8Shell L: Electron 2 of 8Shell L: Electron 3 of 8Shell L: Electron 4 of 8Shell L: Electron 5 of 8Shell L: Electron 6 of 8Shell L: Electron 7 of 8Shell L: Electron 8 of 8MShell M: Electron 1 of 18Shell M: Electron 2 of 18Shell M: Electron 3 of 18Shell M: Electron 4 of 18Shell M: Electron 5 of 18Shell M: Electron 6 of 18Shell M: Electron 7 of 18Shell M: Electron 8 of 18Shell M: Electron 9 of 18Shell M: Electron 10 of 18Shell M: Electron 11 of 18Shell M: Electron 12 of 18Shell M: Electron 13 of 18Shell M: Electron 14 of 18Shell M: Electron 15 of 18Shell M: Electron 16 of 18Shell M: Electron 17 of 18Shell M: Electron 18 of 18NShell N: Electron 1 of 32Shell N: Electron 2 of 32Shell N: Electron 3 of 32Shell N: Electron 4 of 32Shell N: Electron 5 of 32Shell N: Electron 6 of 32Shell N: Electron 7 of 32Shell N: Electron 8 of 32Shell N: Electron 9 of 32Shell N: Electron 10 of 32Shell N: Electron 11 of 32Shell N: Electron 12 of 32Shell N: Electron 13 of 32Shell N: Electron 14 of 32Shell N: Electron 15 of 32Shell N: Electron 16 of 32Shell N: Electron 17 of 32Shell N: Electron 18 of 32Shell N: Electron 19 of 32Shell N: Electron 20 of 32Shell N: Electron 21 of 32Shell N: Electron 22 of 32Shell N: Electron 23 of 32Shell N: Electron 24 of 32Shell N: Electron 25 of 32Shell N: Electron 26 of 32Shell N: Electron 27 of 32Shell N: Electron 28 of 32Shell N: Electron 29 of 32Shell N: Electron 30 of 32Shell N: Electron 31 of 32Shell N: Electron 32 of 32OShell O: Electron 1 of 18Shell O: Electron 2 of 18Shell O: Electron 3 of 18Shell O: Electron 4 of 18Shell O: Electron 5 of 18Shell O: Electron 6 of 18Shell O: Electron 7 of 18Shell O: Electron 8 of 18Shell O: Electron 9 of 18Shell O: Electron 10 of 18Shell O: Electron 11 of 18Shell O: Electron 12 of 18Shell O: Electron 13 of 18Shell O: Electron 14 of 18Shell O: Electron 15 of 18Shell O: Electron 16 of 18Shell O: Electron 17 of 18Shell O: Electron 18 of 18PShell P: Electron 1 of 10Shell P: Electron 2 of 10Shell P: Electron 3 of 10Shell P: Electron 4 of 10Shell P: Electron 5 of 10Shell P: Electron 6 of 10Shell P: Electron 7 of 10Shell P: Electron 8 of 10Shell P: Electron 9 of 10Shell P: Electron 10 of 10QShell Q: Electron 1 of 2Shell Q: Electron 2 of 2ThZ = 90

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):2 / 2 electrons (100%)
Shell L (n=2):8 / 8 electrons (100%)
Shell M (n=3):18 / 18 electrons (100%)
Shell N (n=4):32 / 32 electrons (100%)
Shell O (n=5):18 / 50 electrons (36%)
Shell P (n=6):10 / 72 electrons (14%)
Shell Q (n=7):2 / 98 electrons (2%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d² 7s²

Neutral ground state configuration. Valence electrons: 4.

Atomic & Quantum Properties

Electronegativity (Pauling)1.3 Pauling
1st Ionization Energy587 kJ/mol
Electron Affinity-112 kJ/mol
Atomic Radius (empirical)206 pm
Common Oxidation States+4
Crystal StructureFCC

Physical & Thermal Properties

Density at STP11.72 g/cm³
Melting Point1750 °C (2023 K)
Boiling Point4788 °C (5061 K)
Magnetic OrderingParamagnetic
Discovery Year1829
Discovered ByJöns Jacob Berzelius

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Thorium fuel cycle nuclear reactors breeding fissile Uranium-233 (clean nuclear energy)
  • High-temperature tungsten-thorium TIG welding electrodes (ThO₂ improves arc stability)
  • Incandescent gas camping lantern mantles emitting brilliant white light
  • High-index optical camera lenses
Occurrence in Nature

Abundant in monazite black sand deposits in India, Australia, Brazil, and the United States.

Etymology & Name Origin

Named after Thor, the Norse god of thunder

Important Chemical Compounds
ThO₂ (Thoria / Highest melting oxide at 3390 °C)
Th(NO₃)₄ (Thorium nitrate)
ThF₄ (Thorium tetrafluoride)
Interesting Chemical Facts
  • • Thorium dioxide (ThO₂) has the highest melting point of all known oxides: an astonishing 3,390 °C (6,134 °F).
  • • India holds about 25% of the world's thorium reserves in beach monazite sands, driving its pioneering three-stage nuclear power program.
  • • Thorium is only mildly radioactive (half-life of 14 billion years, equal to the age of the universe) and can be safely held in your hands.
Safety & Handling Note

Weak alpha emitter, but decay products include radioactive Thoron gas (Radon-220); toxic if dust is inhaled.

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