Uranium
Uranium is a dense, naturally occurring radioactive actinide metal with isotopes used in nuclear energy.
Uranium connects ancient rocks with the energy stored in atomic nuclei.
Explore Uranium's atom- Atomic number
- 92
- Standard atomic weight
- 238.02891(3)
- Family
- Actinide
- Period
- 7
- Group
- f-block
- Standard state
- Solid
In everyday life
Uranium is used as fuel in many nuclear power stations.
Something to remember
Natural uranium contains several isotopes, with uranium-238 by far the most abundant.
Meet its electrons
[Rn] 7s2 5f3 6d1
Published neutral-atom ground-state configuration; excited atoms and ions can differ.
Electrons per shell: 2 · 8 · 18 · 32 · 21 · 9 · 2.
The playground shows an illustrative shell model. Real electrons are described by quantum orbitals, rather than tiny planets traveling along fixed paths.
A connection to explore
Uranium and neptunium are neighbouring actinides, named in a planetary sequence.
Meet Neptunium (Np)Properties and conditions
- Standard atomic weight
- 238.02891(3)CIAAW 2024 standard atomic weight (dimensionless). Parentheses give uncertainty in the last quoted digits. Source flags: g m.CIAAW standard atomic weights ↗ · Retrieved 2026-10-15
- Standard state
- SolidPubChem classification, including explicit predictions where stated. Reference temperature and pressure are not supplied in the table.PubChem periodic table ↗ · Retrieved 2026-10-15
- First ionisation energy
- 6.194 eVEnergy to remove the first electron from an isolated neutral gas-phase atom. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electronegativity
- 1.38 Pauling scaleA dimensionless relative measure; values depend on the chosen scale. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Melting point
- 1408 KPubChem reported value. Pressure, allotrope and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Boiling point
- 4404 KPubChem reported value. Pressure and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Density
- 18.95 g/cm³PubChem reported value. Temperature, pressure, allotrope and measurement uncertainty are not specified in the table; gas densities are especially condition-dependent.PubChem periodic table ↗ · Retrieved 2026-10-15
- Oxidation states
- +6, +5, +4, +3Selected PubChem oxidation states; formal electron bookkeeping, not a list of stable free-ion charges or every possible compound.PubChem periodic table ↗ · Retrieved 2026-10-15
- Discovery
- 1789PubChem discovery attribution. Ancient knowledge and competing priority claims cannot always be represented by a single year.PubChem periodic table ↗ · Retrieved 2026-10-15
- Atomic radius
- 240 pmPubChem tabulated radius. Radius definitions depend on bonding and convention; measurement definition and uncertainty are not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electron affinity
- Not reportedPubChem reported gas-phase electron affinity. Sign conventions and electronic states matter; uncertainty is not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
Isotopes, abundance and decay
Isotopes share a proton count but have different neutron counts. This selection includes naturally tabulated compositions and a reference isotope for other elements. It is not a list of every known isotope.
Explore 3 isotopes of U
| Isotope | Relative atomic mass | Natural fraction | Half-life | Decay |
|---|---|---|---|---|
| U-234 | 234.0409523(19) | 0.000054(5) | 245.5 ky (uncertainty 0.6) | ;α=100;SF=1.64e-9 22;28Mg=1.4e-11 3;24Ne+26Ne=9e-12 7 |
| U-235 | 235.0439301(19) | 0.007204(6) | 704 My (uncertainty 1) | ;α=100;SF=7e-9 2;20Ne=8e-10 4;25Ne~8e-10;28Mg=8e-10 |
| U-238Reference isotope | 238.0507884(20) | 0.992742(10) | 4.463 Gy (uncertainty 0.003) | ;α=100;SF=5.44e-5 7;2β−=2.2e-10 3 |
Fractions use NIST’s terrestrial isotopic compositions, which can vary by sample. Parentheses denote uncertainty in the last digits. Half-lives and decay branches use NUBASE2020; # marks estimates, >/< mark limits. “No decay observed” follows that evaluation and does not prove permanent stability. Decay branch intensities are percentages; SF means spontaneous fission, EC electron capture, IT an isomeric transition.
Follow the science
Use these original references to explore the data and context. Atomic weights can vary with isotope composition; values for elements without stable isotopes may describe a representative isotope rather than a standard atomic weight.