# Uranium

Uranium, 00U|  |
| Uranium |
| Pronunciation | /jʊˈreɪniəm/ ​(*yuu-RAY-nee-əm*) |
| Appearance | silvery gray metallic; corrodes to a spalling black oxide coat in air |
|  |
| Standard atomic weight *A*r°(U) |
|  | 238.02891(3) |
|  |
| Uranium in the periodic table |
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|  |  |  |
| --- | --- | --- |
| Hydrogen |  | Helium |
| Lithium | Beryllium |  | Boron | Carbon | Nitrogen | Oxygen | Fluorine | Neon |
| Sodium | Magnesium |  | Aluminium | Silicon | Phosphorus | Sulfur | Chlorine | Argon |
| Potassium | Calcium |  | Scandium | Titanium | Vanadium | Chromium | Manganese | Iron | Cobalt | Nickel | Copper | Zinc | Gallium | Germanium | Arsenic | Selenium | Bromine | Krypton |
| Rubidium | Strontium |  |  | Yttrium | Zirconium | Niobium | Molybdenum | Technetium | Ruthenium | Rhodium | Palladium | Silver | Cadmium | Indium | Tin | Antimony | Tellurium | Iodine | Xenon |
| Caesium | Barium | Lanthanum | Cerium | Praseodymium | Neodymium | Promethium | Samarium | Europium | Gadolinium | Terbium | Dysprosium | Holmium | Erbium | Thulium | Ytterbium | Lutetium | Hafnium | Tantalum | Tungsten | Rhenium | Osmium | Iridium | Platinum | Gold | Mercury (element) | Thallium | Lead | Bismuth | Polonium | Astatine | Radon |
| Francium | Radium | Actinium | Thorium | Protactinium | Uranium | Neptunium | Plutonium | Americium | Curium | Berkelium | Californium | Einsteinium | Fermium | Mendelevium | Nobelium | Lawrencium | Rutherfordium | Dubnium | Seaborgium | Bohrium | Hassium | Meitnerium | Darmstadtium | Roentgenium | Copernicium | Nihonium | Flerovium | Moscovium | Livermorium | Tennessine | Oganesson |

 | Nd ↑ **U** ↓ (Uqh) |
| protactinium ← **uranium** → neptunium |

 |

 |
| Group | f-block groups (no number) |
| Period | period 7 |
| Block |   f-block |
| Electron configuration | [Rn] 5f3 6d1 7s2 |
| Electrons per shell | 2, 8, 18, 32, 21, 9, 2 |
| Physical properties |
| Phase at STP | solid |
| Melting point | 1405.3 K ​(1132.2 °C, ​2070 °F)  |
| Boiling point | 4404 K ​(4131 °C, ​7468 °F)  |
| Density (near r.t.) | 19.1 g/cm3 |
| when liquid (at m.p.) | 17.3 g/cm3  |
| Heat of fusion | 9.14 kJ/mol  |
| Heat of vaporization | 417.1 kJ/mol  |
| Molar heat capacity | 27.665 J/(mol·K)  |
| **Vapor pressure**

| *P* (Pa) | 1 | 10 | 100 | 1 k | 10 k | 100 k |
| --- | --- | --- | --- | --- | --- | --- |
| at *T* (K) | 2325 | 2564 | 2859 | 3234 | 3727 | 4402 |

 |
| Atomic properties |
| Oxidation states | −1, +1, +2, +3, **+4**, +5, **+6** (an amphoteric oxide) |
| Electronegativity | Pauling scale: 1.38  |
| Ionization energies | * 1st: 597.6 kJ/mol
* 2nd: 1420 kJ/mol
*
 |
| Atomic radius | empirical: 156 pm  |
| Covalent radius | 196±7 pm  |
| Van der Waals radius | 186 pm  |
| **Spectral lines of uranium** |
| Other properties |
| Natural occurrence | primordial |
| Crystal structure |  ​orthorhombic |
| Speed of sound  thin rod | 3155 m/s (at 20 °C)  |
| Thermal expansion | 13.9 µm/(m⋅K) (at 25 °C)  |
| Thermal conductivity | 27.5 W/(m⋅K)  |
| Electrical resistivity | 0.280 µΩ⋅m (at 0 °C)  |
| Magnetic ordering | paramagnetic  |
| Young's modulus | 208 GPa  |
| Shear modulus | 111 GPa  |
| Bulk modulus | 100 GPa  |
| Poisson ratio | 0.23  |
| Vickers hardness | 1960–2500 MPa  |
| Brinell hardness | 2350–3850 MPa  |
| CAS Number | 7440-61-1  |
| History |
| Naming | after planet Uranus, itself named after Greek god of the sky Uranus |
| Discovery | Martin Heinrich Klaproth (1789) |
| First isolation | Eugène-Melchior Péligot (1841) |
| Isotopes of uranium* v
* e
 |
|  |
|

| Main isotopes | Decay |
| --- | --- |
|  | abun­dance | half-life (*t*1/2) | mode | pro­duct |
| 232U | synth | 68.9 y | α | 228Th |
| SF | – |
| 233U | trace | 1.592×105 y | α | 229Th |
| SF | – |
| 234U | 0.005% | 2.455×105 y | α | 230Th |
| SF | – |
| 235U | 0.720% | 7.04×108 y | α | 231Th |
| SF | – |
| 236U | trace | 2.342×107 y | α | 232Th |
| SF | – |
| 238U | 99.3% | 4.468×109 y | α | 234Th |
| SF | – |
| β−β− | 238Pu |

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A small amount of uranium in a glass dish
**Uranium** is a chemical element (a metal) on the periodic table. It has an atomic number of 92, which means that a uranium atom has 92 protons in its center, the nucleus.

The Uranium dug out of the ground is made from three different isotopes. The isotopes are different types of uranium with different numbers of neutrons in their nuclei. Most of it is uranium-238; uranium-235 is less common; uranium-234 is the rarest. Pitchblende is the main ore that is mined for uranium.

Uranium-235 can be used in nuclear reactors and nuclear weapons by making a nuclear chain reaction. This turns the uranium-235 into uranium-236 and splits the nucleus into two smaller nuclei. This makes two completely different elements with smaller atomic numbers. The process is called nuclear fission and creates lots of heat. This heat makes it very useful for making steam in nuclear reactors, or for making explosions with nuclear weapons. Most such weapons use plutonium made from uranium-238. Uranium is slightly radioactive.

Uranium without its uranium-235 is called depleted uranium. It is less radioactive than natural uranium. It is used in anti-tank weapons. Uranium can also be used as a dye for stained glass or pottery.

A trefoil radiation warning
Uranium is a dangerous substance. Because uranium is radioactive it is often seen with the hazard sign for radioactive elements, a group of three triangles with curved outer edges pointing in towards the middle (as you can see on the left). Uranium is a shiny white metal, but is usually seen in its oxide form which is black. Spent or partially spent uranium fuel rods are kept underwater, inside a nuclear reactor or in a spent fuel pool. Uranium can glow blue due to Cherenkov radiation. In addition to being radioactive, uranium is a heavy metal and is chemically toxic.

## Characteristics

Uranium is a silvery white, weakly radioactive metal. It has a Mohs hardness of 6. It is malleable, ductile and slightly paramagnetic. It is strongly electropositive. It is a poor electrical conductor. Uranium metal has a very high density of 19.1 g/cm3.

Uranium metal reacts with almost all non-metal elements and their compounds. Hydrochloric and nitric acids dissolve uranium, but non-oxidizing acids other than hydrochloric acid dissolve the element very slowly.

Uranium-235 was the first isotope that was found to be fissile: when it splits, it produces enough neutrons to split other atoms, supporting a nuclear chain-reaction. Other naturally occurring isotopes are fissionable (can be caused to split), but are not fissile.

As little as 15 lb (7 kg) of uranium-235 can be used to make an atomic bomb. The nuclear weapon detonated over Hiroshima, called *Little Boy*, relied on uranium fission.

## History

### Pre-discovery use

The planet Uranus, which uranium is named after
The use of uranium in its natural oxide form dates back to the year 79 AD. It was used in the Roman Empire to make ceramic glazes yellow. Yellow glass with 1% uranium oxide was found in a Roman villa on Cape Posillipo in the Bay of Naples, Italy. It was found by R.T. Gunther of the University of Oxford in 1912. In the late Middle Ages, pitchblende was extracted from the Habsburg silver mines in Joachimsthal, Bohemia (now Jáchymov in the Czech Republic). In the early 19th century, the world's only known sources of uranium ore were these mines.

## Origin

Uranium is only naturally formed by the rapid neutron capture in supernovae and neutron star mergers.

Radioactive heat production is present on Earth in quantities. It may be a widespread component of Solar System planets, and possible other planetary systems. That might help to explain the high internal temperatures of planets.

## Mining

The world's largest producer of uranium is Kazakhstan, which in 2019 produced 43% of the world's mining output. Canada was the next largest producer with a 13% share, followed by Australia with 12%. Uranium has been mined in every continent except Antarctica.