Th Thorium

Quick answerThorium (Th) is an actinide with atomic number 90 and an atomic mass of 232.04 (2023), in period 7. It was discovered by Jöns Jacob Berzelius in 1828. It is used for nuclear fuel research and gas mantles. Its electron configuration is [Rn] 6d2 7s2.

Thorium is a weakly radioactive metal three times more abundant than uranium, and engineers are testing it as a safer nuclear fuel.

Key facts

Symbol	Th
Atomic number	90
Atomic mass	232.04 (IUPAC standard atomic weight, 2023)
Category	actinide
Group	— (f-block element, no group number)
Period	7
Block	f-block
Electron configuration	[Rn] 6d2 7s2
Discovered	Jöns Jacob Berzelius, 1828
Uses	nuclear fuel research, gas mantles, high-temperature ceramics, camera lenses, welding electrodes

Quick quiz

Three questions from the facts on this page. No sign-up, no score is saved.

1. What is the chemical symbol of Thorium?

Ac U Th Pa

2. What is the atomic number of Thorium?

92 90 89 91

3. Which category does Thorium belong to?

halogen actinide noble gas alkali metal

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Keep exploring

• Periodic table — all 118 elements
• Actinium (Ac) — another actinide, atomic number 89
• Protactinium (Pa) — another actinide, atomic number 91
• Uranium (U) — another actinide, atomic number 92
• Neptunium (Np) — another actinide, atomic number 93
• Plutonium (Pu) — another actinide, atomic number 94
• Americium (Am) — another actinide, atomic number 95
• Curium (Cm) — another actinide, atomic number 96
• Berkelium (Bk) — another actinide, atomic number 97
• Californium (Cf) — another actinide, atomic number 98
• Einsteinium (Es) — another actinide, atomic number 99
• All actinide elements — on the periodic table

Sources & last updated

• CIAAW — Standard Atomic Weights
• PubChem Periodic Table
• Wikipedia — Timeline of chemical element discoveries
• Wikipedia — Thorium

Last updated: 2026-11-12. Figures are shown with their year; where sources disagree, the value is left out rather than estimated.