Uranium (U)
Actinide · Radioactive
Uranium is the heaviest element found in nature in significant amounts — and the one that opened the atomic age. Its rare isotope U-235 can sustain a fission chain reaction, powering reactors and, tragically first, weapons.
Position on the periodic table
Atomic properties
| Atomic number | 92 |
|---|---|
| Atomic mass | 238.029 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f3 6d1 |
| Noble gas shorthand | [Rn] 5f3 6d1 7s2 |
| Electrons per shell | 2, 8, 18, 32, 21, 9, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +6, +4 |
| Electronegativity (Pauling) | 1.38 |
| Covalent radius (approx.) | 196 pm |
| First ionization energy | 597.6 kJ/mol |
| Electron affinity | 50.9 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 19.1 g/cm³ |
| Melting point | 1132.2 °C (1405.3 K) |
| Boiling point | 4130.9 °C (4404 K) |
| Appearance | Not available |
| Radioactive | Yes |
| Origin | Occurs naturally |
Electron configuration of uranium
Uranium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f3 6d1, usually shortened to [Rn] 5f3 6d1 7s2. Its electrons occupy 7 shells (2, 8, 18, 32, 21, 9, 2), placing it in period 7 of the f-block. Explore it interactively in the electron configuration calculator.
Uses of uranium
- Nuclear power fuel
- Naval propulsion reactors
- Radiometric dating of rocks
- Radiation shielding and counterweights (depleted uranium)
Biological role: None — chemically toxic to kidneys as well as radioactive.
Occurrence: About 2–3 parts per million of the crust — more common than silver.
Common compounds of uranium
UO2
Uranium dioxide (reactor fuel)
UF6
Uranium hexafluoride (enrichment)
History and discovery
Discovered: 1789 — Martin Heinrich Klaproth. Name origin: Named after the planet Uranus, discovered eight years earlier.
Martin Klaproth identified uranium in pitchblende in 1789; fission was discovered in 1938 by Hahn, Strassmann, Meitner and Frisch.
Safety notes
Both radioactive and chemically toxic; strictly regulated worldwide.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Uranium
1. What is the chemical symbol of Uranium?
2. What is the atomic number of Uranium?
3. Which category does Uranium belong to?
4. What is the state of Uranium at room temperature?
5. Which period of the periodic table is Uranium in?
Uranium FAQs
What is the atomic number of uranium?
Uranium's atomic number is 92 — every uranium atom has 92 protons in its nucleus.
What is the symbol for uranium?
U. Named after the planet Uranus, discovered eight years earlier.
Is uranium a metal, nonmetal, or metalloid?
Uranium is classified as a actinide.
What state is uranium at room temperature?
At about 25 °C, uranium is a solid. It melts at 1132.2 °C.
What is uranium used for?
Key uses include: nuclear power fuel; naval propulsion reactors; radiometric dating of rocks.
Related elements
Keep working with this element
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