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silvery gray; forms a black coating in air
Two hands in brown gloves holding a lump of uranium
General properties
Name, symbol, number uranium, U, 92
Pronunciation /jʊˈrniəm/
Element category actinide
Group, period, block n/a7, f
Standard atomic weight 238.02891(3)g/mol
Electron configuration [Rn] 5f3 6d1 7s2
Electrons per shell 2, 8, 18, 32, 21, 9, 2 (Image)
Physical properties
Phase solid
Density (near r.t.) 19.1 g/cm3
Liquid density at m.p. 17.3 g/cm3
Melting point 1405.3 K, 1132.2 °C, 2070 °F
Boiling point 4404 K, 4131 °C, 7468 °F
Heat of fusion 9.14 kJ/mol
Heat of vaporization 417.1 kJ/mol
Specific heat capacity (25 °C) 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 6, 5, 4, 3,[1] 2, 1
((a weakly
basic oxide))
Electronegativity 1.38 (Pauling scale)
Ionization energies 1st: {{{1st ionization energy}}} kJ/mol
2nd: {{{2nd ionization energy}}} kJ/mol
Atomic radius 156 pm
Covalent radius 196±7 pm
Van der Waals radius 186 pm
Crystal structure orthorhombic
Magnetic ordering paramagnetic
Electrical resistivity (0 °C) 0.280Ω·m
Thermal conductivity (300 K) 27.5 W/(m·K)
Thermal expansion (25 °C) 13.9 µm/(m·K)
Speed of sound (thin rod) (20 °C) 3155 m/s
Young's modulus 208 GPa
Shear modulus 111 GPa
Bulk modulus 100 GPa
Poisson ratio 0.23
CAS registry number 7440-61-1
Most stable isotopes
Main article: Isotopes of uranium
iso NA half-life DM DE (MeV) DP
232U trace 68.9 y SF - -
α 5.414 228Th
{{{dm3}}} {{{de3}}} {{{pn3}}}{{{ps3}}}
233U trace 1.592×105 y SF 197.93[2] -
α 4.909 229Th
{{{dm3}}} {{{de3}}} {{{pn3}}}{{{ps3}}}
234U 0.005% 2.455×105 y SF 197.78 -
α 4.859 230Th
{{{dm3}}} {{{de3}}} {{{pn3}}}{{{ps3}}}
235U 0.720% 7.04×108 y SF 202.48 -
α 4.679 231Th
{{{dm3}}} {{{de3}}} {{{pn3}}}{{{ps3}}}
236U trace 2.342×107 y SF 201.82 -
α 4.572 232Th
{{{dm3}}} {{{de3}}} {{{pn3}}}{{{ps3}}}
238U 99.274% 4.468×109 y α 4.270 234Th
SF 205.87 -
ββ - 238Pu
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.

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). Some people believe that Uranium is light green, and glows. However, this is not true. Uranium is a shiny white metal, but is usually seen in its oxide form which is black.

References[change | change source]

  1. Jump up Morss, L.R.; Edelstein, N.M. and Fuger, J., ed. (2006). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Netherlands: Springer. ISBN 9048131464.
  2. Jump up Proceedings of the conference on nuclear data evaluation methods and procedures. BNL-NCS 51363, vol. II. Upton, NY (USA): Brookhaven National Lab.. 1981. pp. 835 ff. Retrieved 2014-08-06.






Pitchblende schlema-alberoda.JPG

Pitchblende from Niederschlema-Alberoda deposit, Germany



Oxide minerals

(repeating unit)

Uranium dioxide or uranium(IV) oxide (UO2)

Strunz classification


Crystal symmetry

Isometric, hexoctahedral
H-M symbol: (4/m32/m)
Space group: F m3m

Unit cell

a = 5.4682 Å; Z = 4



Steel-black to velvet-black, brownish black, pale gray to pale green; in transmitted light, pale green, pale yellow to deep brown

Crystal habit

Massive, botryoidal, granular. Octahedral crystals uncommon.

Crystal system





Conchoidal to uneven

Mohs scale hardness



Submetallic, greasy, dull


Brownish black, gray, olive-green


Opaque; transparent in thin fragments

Specific gravity

10.63–10.95; decreases on oxidation

Optical properties


Other characteristics

Radioactive: greater than 70 Bq/g



Major varieties



Pitchblende is a radioactive, uranium-rich mineral and ore. It has a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements. It is known as pitchblende due to its black color and high density. It is also commonly referred to as Uraninite. The mineral has been known at least since the 15th century from silver mines in the Ore Mountains, on the German/Czech border. Pitchblende found in Germany was used by M. Klaproth in 1789 to discover the element uranium.[5]

Pitchblende contains a small amount of radium as a radioactive decay product of uranium. Because the uranium isotopes 238U and 235U will decay to form the lead isotopes 206Pb and 207Pb, pitchblende also always contains small amounts of lead. Small amounts of helium are also present in pitchblend as a result of alpha decay. Helium was first found on Earth in pitchblende after having been discovered in the Sun's atmosphere.




Uraninite crystals from Topsham, Maine (size: 2.7×2.4×1.4 cm)

Pitchblende is a major ore of uranium. Some of the highest grade uranium ores in the world were found in the Shinkolobwe mine in the Democratic Republic of the Congo (the initial source for the Manhattan Project) and in the Athabasca Basin in northern Canada. Another important source of pitchblende is at Great Bear Lake in the Northwest Territories of Canada, where it is found in large quantities associated with silver. It also occurs in Australia, Germany, England, and South Africa. In the United States it can be found in the states of New Hampshire, Connecticut, North Carolina, Wyoming, Colorado, Arizona and New Mexico.

Uranium ore is generally processed close to the mine into yellowcake, which is an intermediate step in the processing of uranium.

Related pages


  1. Klein, Cornelis and Cornelius S. Hurlbut, Jr., Manual of Mineralogy, Wiley, 1985, 20th ed. pp. 307–308 ISBN 0-471-80580-7
  2. Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C., ed. "Uraninite" (PDF). Handbook of Mineralogy. III (Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 0-9622097-2-4. Retrieved December 5, 2011.
  3. Uraninite.
  4. Uraninite.
  5. Schüttmann, W. (1998). "Das Erzgebirge und sein Uran". RADIZ-Information 16: 13–34.





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