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/a, 7, 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, 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 -
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 having a neutron fired into its nucleus by humans. 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 symbol
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.


Uranium Facts for Kids. Kiddle Encyclopedia.