Uranium

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Uranium is a silver-gray metallic chemical element in the actinide series of the periodic table that has the symbol U and atomic number 92. It has 92 protons and electrons, 6 of them valence electrons. It can have between 141 and 146 neutrons, with 143 and 146 in its most common isotopes. Uranium has the highest atomic weight of the naturally occurring elements. Uranium is approximately 70% more dense than lead and is weakly radioactive. It occurs naturally in low concentrations (a few parts per million) in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite (see uranium mining).

 

General
Name, symbol, number uranium, U, 92
Chemical series actinides
Group, period, block n/a, 7, f
Appearance silvery gray metallic;
corrodes to a spalling
black oxide coat in air
Standard atomic weight 238.02891(3)g·mol-1
Electrons per shell 2, 8, 18, 32, 21, 9, 2
Physical properties
Phase solid
Density (near r.t.) 19.1 g·cm−3
Liquid density at m.p. 17.3 g·cm−3
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-1
Heat of vaporization 417.1 kJ·mol-1
Heat capacity (25 °C) 27.665 J·mol-1·K-1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2325 2564 2859 3234 3727 4402
Atomic properties
Crystal structure orthorhombic
Oxidation states 3+,4+,5+,6+
(weakly basic oxide)
Electronegativity 1.38 (Pauling scale)
Ionization energies 1st: 597.6 kJ·mol-1
2nd: 1420 kJ·mol-1
Atomic radius 175 pm
Van der Waals radius 186 pm
Miscellaneous
Magnetic ordering paramagnetic
Electrical resistivity (0 °C) 0.280 µΩ·m
Thermal conductivity (300 K) 27.5 W·m-1·K-1
Thermal expansion (25 °C) 13.9 µm·m-1·K-1
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

 

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