Periodic table › Uranium
Uranium — U
Actinoid · Group Actinoid (f-block) · Period 7
Open the 3D atom, orbital and crystal lab →1. Identity and classification
Silvery-grey, very dense, weakly radioactive metallic solid; tarnishes rapidly in air to a dark oxide coat
- Name and symbol
- Uranium (Uranium) · U
- Atomic number
- 92
- Relative atomic weight / mass number
- 238.03 ± 0.01
- Group · period · block
- Actinoid (f-block) · 7 · f
- Category
- Actinoid
- State near room temperature
- Solid
- Stable isotopes
- No stable isotopes
- CAS number
- 7440-61-1
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 92 · 92
- Neutrons in reference isotope
- 146 (238U)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f³ 6d¹ 7s²- Abbreviated configuration
[Rn]7s² 5f³ 6d¹- Electrons per shell
- 2, 8, 18, 32, 21, 9, 2
- Listed oxidation states
- +6, +5, +4, +3
- Electronegativity
- 1.38 (Pauling)
- First ionization energy
- 597.63 kJ/mol · 6.194 eV
- Electron affinity
- Not established
- Covalent radius
- 196 pm
- van der Waals radius
- 240 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 18.95 g/cm³
- Melting point
- 1408 K · 1134.85 °C · 2074.73 °F
- Boiling point
- 4404 K · 4130.85 °C · 7467.53 °F
- Crystal structure
- Orthorhombic
- Specific heat
- 0.116 J/(g·K)
- Thermal conductivity
- 27.5 W/(m·K)
- Enthalpy of fusion
- 9.14 kJ/mol
- Enthalpy of vaporization
- 417.1 kJ/mol
- Magnetic ordering
- Paramagnetic
- Mohs hardness
- 6
- Speed of sound
- 3155 m/s
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The +3 state is common in this series, with important element-specific exceptions.
Selected compounds: UO₂ (Uranium dioxide nuclear fuel) · UF₆ (Uranium hexafluoride) · U₃O₈ (Yellowcake)
Reaction reference
Many members oxidize in air; behavior depends on the element and oxidation state.
Water reactivity varies across this series and with surface conditions.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 234U | Radioactive | 0.0054% | 2.455E+5 Y |
| 235U | Radioactive | 0.7204% | 7.04E+8 Y |
| 238U | Radioactive | 99.2742% | 4.468E9 Y |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- 1789 CE
- Scientists associated with discovery
- Martin Heinrich Klaproth
- Location
- Germany (Berlin)
- Origin
- Natural
- Listed crustal abundance
- 2.7 ppm
Minerals and naming reference
Uraninite / Pitchblende (UO₂), Carnotite, Autunite, Coffinite, Brannerite
Named in 1789 by Martin Heinrich Klaproth after the planet Uranus, which had been discovered eight years earlier by William Herschel
7. Applications
Historically used in fluorescent yellow-green Vaseline/uranium glass and ceramic glazes
Detailed applications by field
- everyday
- Historically used in fluorescent yellow-green Vaseline/uranium glass and ceramic glazes
- industry
- High-density radiation shielding containers for industrial gamma radiography sources
- electronics
- Specialized electron microscope staining (uranyl acetate for biological ultrastructure)
- medicine
- Target material for producing molybdenum-99 / technetium-99m medical diagnostic radioisotopes
- energy
- Primary fissile (²³⁵U) and fertile (²³⁸U) nuclear fuel powering commercial pressurized and boiling water reactors worldwide
- aerospace
- Counterweights in aircraft control surfaces; radioisotope space power systems research
- agriculture
- Radiometric dating of soils and groundwater hydrology via uranium-series disequilibrium
- science
- U-Pb radiometric geochronology of zircon crystals to determine the age of Earth (4.54 billion years)
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
No biological role; acts primarily as a chemical nephrotoxin (heavy-metal kidney toxicity) in addition to its radiological alpha-particle hazard if inhaled or ingested.