Uranium vs Thorium
Both are actinides, so they share the same broad chemistry.
The differences in plain English
- They sit in the same column, group 3, so they have the same number of outer electrons and react in similar ways; the heavier one, Uranium, is usually the more reactive of the two if they are metals, and the less reactive if they are non-metals.
- Both are solids at room temperature.
- Uranium is denser, about 63 per cent more than Thorium (19.1 against 11.724 g/cm³).
- Thorium melts at 1750 °C, far above Uranium at 1132 °C.
- An atom of Uranium is only slightly heavier than an atom of Thorium (238.03 u against 232.04 u).
- Uranium pulls electrons more strongly in a bond (electronegativity 1.38 against 1.3).
Side by side
| Uranium | Thorium | |
|---|---|---|
| Atomic number | 92 | 90 |
| Symbol | U | Th |
| Family | Actinide | Actinide |
| Group / period | 3 / 7 | 3 / 7 |
| State at room temperature | Solid | Solid |
| Atomic mass | 238.029 u | 232.038 u |
| Density | 19.1 g/cm³ | 11.724 g/cm³ |
| Melting point | 1132 °C | 1750 °C |
| Boiling point | 4131 °C | 4788 °C |
| Electronegativity | 1.38 | 1.3 |
| First ionisation energy | 597.6 kJ/mol | 587 kJ/mol |
| Electron configuration | [Rn] 5f3 6d1 7s2 | [Rn] 6d2 7s2 |
| Discovered by | Martin Heinrich Klaproth | Jöns Jakob Berzelius |
Uranium
Uranium is a dense, silvery-grey metal that most people know for a single reason: it can be split. When a uranium-235 nucleus captures a neutron it breaks in two, releases a burst of energy and throws out more neutrons that can split further nuclei. That chain reaction runs every nuclear power station on Earth and was the basis of the first atomic weapons.
- Uranium-238 has a half-life of about 4.5 billion years, almost exactly the age of the Earth, so roughly half the uranium the planet started with is still here.
- Uranium glass, popular from the 1830s to the 1940s, fluoresces bright green under ultraviolet light, and collectors still hunt for it at car boot sales.
Thorium
Thorium is a soft, silvery metal that has spent two centuries being almost useful. It lit streets and campsites, sharpened camera lenses and strengthened aircraft engines. Now it is best known for a job it has never quite landed: powering nuclear reactors that would be cleaner and safer than uranium ones.
- Thorium-232 has a half-life of about 14 billion years, roughly the age of the universe, so around 80 per cent of the thorium present when the Earth formed is still here.
- The decay of thorium, uranium and potassium in the Earth's interior produces a large share of the heat that drives plate tectonics and volcanoes.
Colour the bubbles by density or melting point and the difference jumps out.
More comparisons
Data from Periodic-Table-JSON (CC BY-SA); temperatures rounded to the nearest degree. Written by Anthony.