Uranium

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.

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 Ar°(U)
	238.02891(3)
Uranium in the periodic table
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
Main isotopes Decay abun­dance half-life (t1/2) 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

A small amount of uranium in a glass dish

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: The molecule splits. Other naturally occurring isotopes are fissionable (can be broken down), 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

See the main article: Uranium 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.