Uranium (U)

Isotopes of Uranium

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin Nuclear Magnetic Moment
U-230  230.03393  20.80 days  α to Th-226 0  No data available 
U-231  231.03626  4.20 days  α to Th-227 5/2  No data available 
U-232 232.03715 68.90 years α to Th-228 0 No data available 
U-233 233.039628 1.59 x 105 years α to Th-229; SF 5/2 0.59
U-234 234.0409468 2.45 x 105 years α to Th-230; SF 0 No data available 
U-235 235.0439242 7.04 x 108 years α to Th-231; SF 7/2 0.38
U-236 236.045561 2.34 x 107 years α to Th-232; SF 0 No data available 
U-237 237.048723 6.75 days β- to Np-237 1/2 No data available 
U-238 238.0507847 4.46 x 109 years α to Th-234; SF 0 No data available 

U

Uranium was discovered in 1789 by Martin Heinrich Klaproth and named after the planet Uranus, which had just been discovered. It was isolated in 1841 by Eugène-Melchior Péligot, and its radioactive properties were discovered in 1896 by Henri Becquerel.

The heaviest naturally-occurring element, uranium is a silvery-white metal that is malleable, ductile and slightly paramagnetic. The metal exists in three crystal forms: an orthorhombic alpha phase with a density of 18.97 g/cm3 and stable up to 667 ºC, a tetragonal beta phase with density of 18.11 g/cm3 and stable from 688-776 ºC, and a body-centered cubic form with a density of 18.06 g/cm3 and stable in the range of 776-1132 ºC. It is insoluble in water and alkalis and soluble in acids. Uranium metal reacts with almost all nonmetallic elements and their compounds, its reactivity increasing with temperature. Hydrochloric and nitric acids dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element very slowly. When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of uranium oxide. Uranium in ores is extracted chemically and converted into uranium dioxide or other chemical forms usable in industry.

The major application of uranium in the military sector is in high-density penetrators. This ammunition consists of depleted uranium (DU) alloyed with 1–2% other elements. Depleted uranium is also used as a shielding material in some containers that store and transport radioactive materials. Uranium-235 has been used as the fissile explosive material to produce nuclear weapons. The main use of uranium in the civilian sector is to fuel nuclear power plants: one kilogram of Uranium-235 can theoretically produce as much energy as 3000 tonnes of coal. Uranium has also been used in small amounts for yellow glass and pottery glazes, such as uranium glass and in Fiesta® dinnerware.

Uranium is a toxic metal. Exposure can affect kidneys, brain, liver, heart and other systems. The metal is commonly handled with gloves as a precaution; uranium concentrate is handled and contained in order to prevent its inhalation or ingestion.

Properties of Uranium

Name Uranium 
Symbol U 
Atomic number 92 
Atomic weight 238.02891 
Standard state Solid at 298 ºK 
CAS Registry ID 7440-61-1 
Group in periodic table N/A 
Group name Actinoid 
Period in periodic table 7 (Actinoid) 
Block in periodic table f-block 
Color Metallic gray 
Classification Metallic 
Melting point 1132.2 °C
Boiling point 3900 °C
Vaporization point 4131 °C
Thermal conductivity 27.6  W/(m·K)
Electrical resistivity 28 x 10-8 Ω·m 
Electronegativity 1.38 
Heat of vaporization 420 kJ·mol-1
Heat of fusion 14 kJ·mol-1
Density of liquid 17.3 g/cm3 at 1132.2 °C
Density of solid 19.05 g/cm3 
Electron configuration [Rn]5f36d17s2 
Ionic radii U3+: 1.03 Å, U4+: 0.89 Å, U5+: 0.76 Å (coordination number 6);
U6+: 0.45 Å (coordination number 2);
U6+: 0.81 Å (coordination number 7)
Oxidation states  +2, +3, +4, +4, +5, +6 

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