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# Uranium

Uranium,  92U
General properties
Pronunciation
Appearancesilvery gray metallic; corrodes to a spalling black oxide coat in air
Standard atomic weight (Ar, standard)238.02891(3)[1]
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)
protactiniumuraniumneptunium
92
Groupgroup n/a
Periodperiod 7
Blockf-block
Element category  actinide
Electron configuration[Rn] 5f3 6d1 7s2
Electrons per shell
2, 8, 18, 32, 21, 9, 2
Physical properties
Phase at STPU: Solid
Melting point1405.3 K ​(1132.2 °C, ​2070 °F)
Boiling point4404 K ​(4131 °C, ​7468 °F)
Density (near r.t.)19.1 g/cm3
when liquid (at m.p.)17.3 g/cm3
Heat of fusion9.14 kJ/mol
Heat of vaporization417.1 kJ/mol
Molar heat capacity27.665 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, +2, +3,[2] +4, +5, +6 (a weakly basic oxide)
ElectronegativityPauling scale: 1.38
Ionization energies
• 1st: 597.6 kJ/mol
• 2nd: 1420 kJ/mol
Spectral lines of uranium
Other properties
Natural occurrenceU: Primordial
Crystal structureorthorhombic
Speed of sound thin rod3155 m/s (at 20 °C)
Thermal expansion13.9 µm/(m·K) (at 25 °C)
Thermal conductivity27.5 W/(m·K)
Electrical resistivity0.280 µΩ·m (at 0 °C)
Magnetic orderingparamagnetic
Young's modulus208 GPa
Shear modulus111 GPa
Bulk modulus100 GPa
Poisson ratio0.23
Vickers hardness1960–2500 MPa
Brinell hardness2350–3850 MPa
CAS Number7440-61-1
History
Namingafter planet Uranus, itself named after Greek god of the sky Uranus
DiscoveryMartin Heinrich Klaproth (1789)
First isolationEugène-Melchior Péligot (1841)
Main isotopes of uranium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
232U syn 68.9 y SF
α 228Th
233U trace 1.592×105 y SF
α 229Th
234U 0.005% 2.455×105 y SF
α 230Th
235U 0.720% 7.04×108 y SF
α 231Th
236U trace 2.342×107 y SF
α 232Th
238U 99.274% 4.468×109 y α 4.270 234Th
SF 205.87
ββ 238Pu
| references
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, which is called a nucleus. Uranium that is dug out of the ground will be made from three different isotopes: three 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. This 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. But most such weapons use Plutonium made from uranium-238. Uranium is a bit radioactive.

Uranium which has had its uranium-235 taken out of it is called depleted uranium. It is used in anti-tank weapons. Uranium can also be used as a dye for stained glass or pottery, which is how it was used before people found out that it was radioactive.

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). Some people believe that Uranium is light green, and glows, due to the way it is depicted in many movies. However, this is not true. Uranium is a shiny white metal, but is usually seen in its oxide form which is black. Spent or partially spent uranium fuel rods kept underwater, for example inside a nuclear reactor or in a spent fuel pool, 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.[4][5] Uranium metal has a very high density of 19.1 g/cm3.[6]

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.[4]

Uranium-235 was the first isotope that was found to be fissile. Other naturally occurring isotopes are fissionable, but 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 CE. It was used in the Roman Empire to make ceramic glazes yellow.[5] 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.

## References

1. Meija, J.; Coplen, T. B.; Berglund, M.; Brand, W.A.; De Bièvre, P.; Gröning, M.; Holden, N.E.; Irrgeher, J. et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry 88 (3): 265-91. .
2. The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Netherlands: Springer. 2006. .
3. The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Netherlands: Springer. 2006. .
4. McGraw-Hill concise encyclopedia of science & technology. (5th ed ed.). New York: McGraw-Hill. 2005. . .
5. CRC handbook of chemistry and physics, 2000-2001. Lide, David R., 1928- (81st ed ed.). Boca Raton: CRC Press. 2000. . .