Uranium
[Rn] 5f³ 6d¹ 7s² · 2 · 8 · 18 · 32 · 21 · 9 · 2
The heaviest element found on Earth in industrial quantity, and the only natural nuclide that will sustain a fission chain reaction. Uranium-235 is just 0.72 % of natural uranium, and the whole of nuclear power rests on separating it out.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 92
- Atomic mass
- 238.029 а.е.м.
- Electron configuration
- [Rn] 5f³ 6d¹ 7s²
- Electrons per shell
- 2 · 8 · 18 · 32 · 21 · 9 · 2
- Block
- f-block
- Group
- no data
- Period
- 7
- Electronegativity (Pauling)
- 1.38
- Electronegativity (Allen)
- 1.22
- Atomic radius
- 240 pm
- Covalent radius
- 196 pm
- Van der Waals radius
- 186 pm
- Ionisation energy 1
- 597.6 kJ/mol
- Ionisation energy 2
- 1 420 kJ/mol
- Electron affinity
- 50.9 kJ/mol
- Common oxidation states
- +6
- Oxidation states
- +1, +2, +3, +4, +5, +6
Physical properties
- State at 25 °C
- solid
- Density
- 19.1 g/cm³
- Melting point
- 1 405.3 K · 1 132.2 °C
- Boiling point
- 4 404 K · 4 130.9 °C
- Speed of sound
- 3 155 m/s
Thermal properties
- Heat of fusion
- 9.14 kJ/mol
- Heat of vaporisation
- 417.1 kJ/mol
- Specific heat capacity
- 0.116 J/(g·K)
- Thermal conductivity
- 27.5 W/(m·K)
Mechanical properties
- Young's modulus
- 208 GPa
- Shear modulus
- 111 GPa
- Bulk modulus
- 100 GPa
- Poisson ratio
- 0.23
- Mohs hardness
- 6
- Brinell hardness
- 2 400 MPa
Electrical and magnetic properties
- Electrical resistivity
- 280 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 0.2 K
Crystal structure
- Crystal structure
- orthorhombic
- Lattice constants
- a = 285.4 pm · b = 587 pm · c = 495.6 pm
Abundance
- In the crust
- 2.7 mg/kg
- In the ocean
- 0.0032 mg/L
- In the universe
- 0.0002 mg/kg
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 234U | 0.0054 % | 245 524.35 yr | α |
| 235U | 0.7204 % | 703.81 Myr | α |
| 238U | 99.274 % | 4.47 Gyr | α |
Uranium-238 is 99.27 % and does not fission on thermal neutrons, but captures them and becomes plutonium-239. Uranium-235 (0.72 %) is the only natural fissile nuclide.
Discovery
- Year of discovery
- 1789
- Discovered by
- Martin Heinrich Klaproth
- Where
- Germany
- Origin of the name
- after the planet Uranus, discovered eight years earlier
History
Klaproth isolated the oxide in 1789 from pitchblende and named it after the newly discovered planet Uranus. Becquerel found uranium's radioactivity in 1896 by accidentally leaving a uranium salt on a photographic plate in a drawer.
Where it occurs
2.7 mg/kg of the crust — commoner than silver or mercury. Some 4.5 billion tonnes of uranium are dissolved in seawater.
How it is produced
By mining and in-situ leaching, then processing to yellowcake and enrichment by centrifuging the hexafluoride.
Role in living things
No biological role. Uranium is chemically toxic to the kidneys much as lead is, quite apart from its radioactivity.
Safety
A double hazard: chemical kidney toxicity and radiological risk from inhaled aerosols. Depleted uranium in munitions remains contested with respect to long-term health effects.
Uses
- Nuclear reactor fuel — about 10 % of world electricity
- Nuclear weapons
- Depleted uranium in armour-piercing penetrators and aircraft balance weights
- Uranium-lead dating of the oldest rocks
- Uranium glass, which fluoresces green under ultraviolet (historical)
Curiosities
- A natural nuclear reactor ran at Oklo in Gabon two billion years ago, when the uranium-235 fraction was still high enough to go critical.
- The age of the Earth — 4.54 billion years — was first measured precisely from uranium-lead isotope ratios.
- Nineteenth-century uranium glass is still safe to handle but fluoresces brilliantly under ultraviolet.
- Becquerel discovered radioactivity by accident: cloudy weather made him put the uranium salt and the plate away in a drawer.