Atomic Number
90
Element 90
Thorium (Th)
Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only three radioactive elements that still occur naturally in large quantities as a primordial element.
Atomic Mass
232.04 u
Category
Actinide
Period
7
Group
Actinide series
Phase
solid
Density
11.7 g/cm3
Electron Shells
2, 8, 18, 32, 18, 10, 2
Atomic Structure
Protons: 90. Electrons: 90. Neutrons: Varies by isotope.
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 6d²
Why Thorium Matters
Thorium helps connect atomic number 90, actinide behavior, period 7 trends, and electron shell structure. Its solid phase, atomic mass of 232.04 u, and electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 6d² make it useful for comparing bonding patterns across the periodic table.
Discovery and Occurrence
Thorium was discovered 1829 by Jöns Jakob Berzelius. Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only three radioactive elements that still occur naturally in large quantities as a primordial element.
Safety and Handling Context
Thorium has radioactive isotopes or is commonly discussed with radioactive materials. Use this page as an educational reference; real samples require qualified supervision and controlled handling.
Related Elements
Frequently Asked Questions
- What is the atomic number of Thorium?
- Thorium has atomic number 90, which means a neutral atom has 90 protons and 90 electrons.
- What is the chemical symbol for Thorium?
- The chemical symbol for Thorium is Th.
- What category is Thorium in?
- Thorium is classified as a actinide and sits in period 7 of the periodic table.
Explore Thorium in 3D
Use the interactive table above to rotate atomic models, compare periodic trends, and move from Thorium to neighboring elements without losing your place.