Uranium
Uranium (U) is element 92, an actinide in period 7 of the f-block, with an atomic mass of 238.0289 u. It is a solid at room temperature and melts at 1134.85 °C. Its electron configuration is [Rn] 7s² 5f³ 6d¹.
Uranium is a dense, silvery-white metal and the heaviest element found on Earth in more than trace amounts. It's mildly radioactive in its natural form, decaying extremely slowly, but it owes its fame to a rarer isotope, uranium-235, which can sustain a nuclear chain reaction — the basis of both nuclear power and the first atomic weapons.
- Group · Period
- — · 7
- At room temp
- solid
- Melts at
- 1408 K
- Density
- 18.95 g/cm³
- Discovered
- 1789
Key facts about uranium
Quick answers, built from the sourced data in the property tables.
- What is the electron configuration of uranium?
- The electron configuration of uranium is [Rn] 7s² 5f³ 6d¹. Written out in full, that is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 7s² 5f³ 6d¹. It is one of the exceptions to the usual aufbau filling order.
- What is the density of uranium?
- The density of uranium is 18.95 g/cm³.
- What are the melting and boiling points of uranium?
- Uranium melts at 1408 K (1134.85 °C, 2074.73 °F) and boils at 4404 K (4130.85 °C, 7467.53 °F).
- What is the longest-lived isotope of uranium?
- Uranium has no stable isotopes. Its longest-lived known isotope is U-238, with a half-life of 4.468 × 10⁹ years.
Uses
Uranium’s defining modern use is as nuclear fuel: uranium-235, enriched to usable concentrations, sustains the chain reactions that power nuclear plants generating electricity for hundreds of millions of people, and in far more concentrated form formed the core of the first atomic weapons. Depleted uranium — what’s left after enrichment, mostly uranium-238 — is dense enough to be used in armor-piercing ammunition and as counterweights in aircraft, applications that rely on its weight rather than its radioactivity.
Long before any of that was possible, uranium had a much quieter role: its compounds were prized for coloring glass and ceramic glazes a distinctive yellow-green, an industry that predates any understanding of radioactivity and largely ended once the risks became clear.
History
Uranium was identified in 1789 by German chemist Martin Heinrich Klaproth, who found a new element in the mineral pitchblende and named it after the planet Uranus. The pure metal wasn’t isolated until 1841, by French chemist Eugène-Melchior Péligot. Uranium’s most consequential chapter began in 1896, when Henri Becquerel noticed that uranium salts fogged photographic plates without any light source — the discovery of radioactivity. Decades later, the 1938 discovery that uranium nuclei could be split, and the realization that this fission could release enormous energy, set in motion the research that led to both nuclear power and nuclear weapons.
Fun facts
- Uranium was the very substance in which radioactivity was first detected, by Henri Becquerel in 1896, years before the phenomenon even had a name.
- Natural uranium is over 99% uranium-238, with less than 1% of the fissile uranium-235 that reactors and weapons need — which is why it must be enriched.
- Uranium glass, popular in the early 20th century, contains trace uranium that makes it glow bright green under ultraviolet light.
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Frequently asked questions
Is all uranium radioactive?
Yes, every isotope of uranium is radioactive, though most decay extremely slowly. Natural uranium's dominant isotope, uranium-238, has a half-life of about 4.5 billion years — roughly the age of the Earth — so a lump of it is only mildly radioactive to handle.
Why does nuclear fuel need to be 'enriched'?
Reactors and weapons rely on uranium-235, the isotope that splits easily when struck by a neutron, but natural uranium contains less than 1% of it. Enrichment concentrates the uranium-235 fraction — typically to a few percent for power reactors, far higher for weapons — through processes like gas centrifuges.
Why is uranium named after a planet?
German chemist Martin Klaproth named it after Uranus, which had been discovered just eight years earlier, in 1781. It followed a chemistry tradition of the time of naming new discoveries after new astronomical ones.
Compounds
4 notable compounds containing U
- U3O8oxide
Triuranium octoxide
A dark green-black mixed-valence oxide containing uranium in both the +5 and +6 states, and the thermodynamically most stable uranium oxide in air across a wide temperature range. It's the form uranium ore concentrate settles into after milling.
Used for: Standard storage and shipping form of milled uranium ore ("yellowcake")
- UO2oxide
Uranium dioxide
A black, ceramic solid with a fluorite crystal structure in which each uranium atom sits surrounded by eight oxygen atoms. It's the most thermally and chemically stable uranium oxide, holding its solid form up to temperatures near 2865°C.
Used for: Fuel pellets in nuclear power reactors
- UF6halide
Uranium hexafluoride
A volatile, colorless solid that sublimes readily and turns into a dense, corrosive gas just above room temperature. Its six fluorine atoms make it the only uranium compound volatile enough to be processed by gas centrifuge or diffusion.
Used for: Feedstock gas for uranium enrichment
- UF4halide
Uranium tetrafluoride
A green, non-volatile crystalline solid nicknamed "green salt," made by reacting uranium oxide with hydrofluoric acid. It's the intermediate step between uranium oxide and the volatile hexafluoride used for enrichment.
Used for: Intermediate in uranium enrichment and uranium metal production
Isotopes
40 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width | Spin/parity | Magnetic moment | Quadrupole moment |
|---|---|---|---|---|---|---|---|---|---|
| U-234 | 0.0054% | 2.455E+5 Y | Alpha decay (100%), Spontaneous fission (1.64e-9%), Mg (1.4e-11%) | 38,144.96 keV | 7,600.72 keV | 5.89 × 10-29 eV | 0+ | — | — |
| U-235 | 0.7204% | 7.04E+8 Y | Alpha decay (100%), Spontaneous fission (7e-9%), {+25}Ne (8e-10%) | 40,918.78 keV | 7,590.92 keV | 2.05 × 10-32 eV | 7/2- | -0.38 μN | 4.936 b |
| U-238 | 99.2742% | 4.468E9 Y | Alpha decay (100%), Spontaneous fission (0.0000545%) | 47,307.73 keV | 7,570.13 keV | 3.24 × 10-33 eV | 0+ | — | — |
| U-214 | — | 0.52 ms | Alpha decay (100%) | — | — | 8.77 × 10-13 eV | 0+ | — | — |
| U-215 | — | 0.7 ms | Alpha decay (0%), Electron capture / beta-plus decay | 24,889.31 keV | 7,620.78 keV | 6.52 × 10-13 eV | — | — | — |
| U-216 | — | 4.5 ms | Alpha decay (100%) | 23,066.43 keV | 7,631.31 keV | 1.01 × 10-13 eV | 0+ | — | — |
| U-217 | — | 16 ms | Alpha decay (100%), Electron capture / beta-plus decay | 22,971 keV | 7,634 keV | 2.85 × 10-14 eV | — | — | — |
| U-218 | — | 0.65 ms | Alpha decay (100%) | 21,894.66 keV | 7,640.72 keV | 7.02 × 10-13 eV | 0+ | — | — |
| U-219 | — | 60 us | Alpha decay (100%) | 23,295.95 keV | 7,636.29 keV | 7.60 × 10-12 eV | — | — | — |
| U-221 | — | 0.66 us | Alpha decay (100%) | 24,520 keV | 7,634.68 keV | 6.91 × 10-10 eV | (9/2+) | — | — |
| U-222 | — | 4.7 us | Alpha decay (100%) | 24,272.83 keV | 7,637.77 keV | 9.71 × 10-11 eV | 0+ | — | — |
| U-223 | — | 18 us | Alpha decay (100%), Electron capture / beta-plus decay (0.2%) | 26,045.28 keV | 7,631.76 keV | 2.53 × 10-11 eV | — | — | — |
| U-224 | — | 396 us | Alpha decay (100%) | 25,742.69 keV | 7,635.07 keV | 1.15 × 10-12 eV | 0+ | — | — |
| U-225 | — | 69 ms | Alpha decay (100%) | 27,372 keV | 7,629.77 keV | 6.61 × 10-15 eV | — | — | — |
| U-226 | — | 268 ms | Alpha decay (100%) | 27,328.8 keV | 7,631.92 keV | 1.70 × 10-15 eV | 0+ | — | — |
| U-227 | — | 1.1 m | Alpha decay (100%) | 29,045.03 keV | 7,626.29 keV | 6.91 × 10-18 eV | (3/2+) | — | — |
| U-228 | — | 9.1 m | Alpha decay (95%), Electron capture (5%) | 29,220 keV | 7,627.48 keV | 8.36 × 10-19 eV | 0+ | — | — |
| U-229 | — | 58 m | Electron capture (80%), Alpha decay (20%) | 31,210.62 keV | 7,620.72 keV | 1.31 × 10-19 eV | (3/2+) | — | — |
| U-230 | — | 20.23 d | Alpha decay (100%), {+22}Ne (4.8e-12%) | 31,615.02 keV | 7,620.92 keV | 2.61 × 10-22 eV | 0+ | — | — |
| U-231 | — | 4.2 d | Electron capture (100%), Alpha decay (0.004%) | 33,805.95 keV | 7,613.39 keV | 1.26 × 10-21 eV | (5/2-) | — | — |
| U-232 | — | 68.9 Y | Alpha decay (100%), {+24}Ne (8.9e-10%), Spontaneous fission (2.7e-12%) | 34,609.45 keV | 7,611.9 keV | 2.10 × 10-25 eV | 0+ | — | — |
| U-233 | — | 1.5919E5 Y | Alpha decay (100%), 24NE (7.2e-11%), Spontaneous fission (6e-11%) | 36,919.11 keV | 7,603.96 keV | 9.08 × 10-29 eV | 5/2+ | -0.59 μN | 3.663 b |
| U-236 | — | 2.342E7 Y | Alpha decay (100%), Spontaneous fission (9.4e-8%) | 42,444.58 keV | 7,586.49 keV | 6.17 × 10-31 eV | 0+ | — | — |
| U-237 | — | 6.752 d | Beta-minus decay (100%) | 45,390.13 keV | 7,576.1 keV | 7.82 × 10-22 eV | 1/2+ | — | — |
| U-239 | — | 23.45 m | Beta-minus decay (100%) | 50,572.67 keV | 7,558.56 keV | 3.24 × 10-19 eV | 5/2+ | — | — |
| U-240 | — | 14.1 h | Beta-minus decay (100%) | 52,715.5 keV | 7,551.77 keV | 8.99 × 10-21 eV | 0+ | — | — |
| U-241 | — | — | Beta-minus decay | 56,197 keV | 7,539 keV | — | — | — | — |
| U-242 | — | 16.8 m | Beta-minus decay (100%) | 58,620 keV | 7,532 keV | 4.53 × 10-19 eV | 0+ | — | — |
| U-243 | — | — | Beta-minus decay | 62,480 keV | 7,518 keV | — | — | — | — |
| U-244 | — | — | Beta-minus decay | — | — | — | 0+ | — | — |
| U-245 | — | — | Beta-minus decay | — | — | — | — | — | — |
| U-246 | — | — | Beta-minus decay | — | — | — | 0+ | — | — |
| U-247 | — | — | Beta-minus decay | — | — | — | — | — | — |
| U-248 | — | — | Beta-minus decay | — | — | — | 0+ | — | — |
| U-249 | — | — | Beta-minus decay | — | — | — | — | — | — |
| U-250 | — | — | Beta-minus decay | — | — | — | 0+ | — | — |
| U-251 | — | — | Beta-minus decay | — | — | — | — | — | — |
| U-253 | — | — | Beta-minus decay, Beta-minus, neutron emission | — | — | — | — | — | — |
| U-254 | — | — | Beta-minus decay (100%), Beta-minus, neutron emission | — | — | — | 0+ | — | — |
| U-255 | — | — | Beta-minus decay, Beta-minus, neutron emission | — | — | — | — | — | — |
Spin/parity describes the nucleus's intrinsic angular momentum and symmetry. Magnetic moment (in nuclear magnetons, μN) and quadrupole moment (in barns, b) describe the shape of the nucleus's charge distribution — a nonzero quadrupole moment means the nucleus isn't perfectly spherical. These are only measured for a subset of isotopes, mostly stable or long-lived ones, so many rows show "—" rather than a value.