URANIUM

TRANSITION ELEMENT: ACTINIDE

Atomic number:	92
Group numbers:	3
Period:	7
Electronic configuration:	[Rn] 5f³ 6d¹ 7s²
Formal oxidation number:	+3 +4 +5 +6
Electronegativities:	1.7
Atomic radius / pm:	138.5
Relative atomic mass:	238.028 91(3)

Uranium was discovered by Martin Heinrich Klaproth (DE) in 1789. Named after the planet Uranus. It is a silvery-white, dense, ductile, malleable, radioactive, radiotoxic metal that resists alkalis, tarnishes in air and reacts with steam and acids. Uranium occurs in many rocks, but in large amounts only in such minerals as pitchblende and carnotite. For many centuries it was used as a pigment for glass. Now it is used as a fuel in nuclear reactors and in bombs. The price of 99.7 % pure uranium turnings is 217.60 € for 25 g.

PHYSICAL PROPERTIES
Density / g dm^-3:	18950	(293 K)
	17907	(m.p.)
Molar volume / cm³mol^-1:	12.56	(293 K)
	13.29	(m.p.)
Electrical resistivity / µΩcm:	30	(20 °C)

THERMAL PROPERTIES
Thermal conductivity / W m^-1K^-1:	27.6
Melting point / °C:	1135
Boiling point / °C:	4131
Heat of fusion / kJ mol^-1:	15.5
Heat of vaporization / kJ mol^-1:	417.1
Heat of atomization / kJ mol^-1:	535.43

IONIZATION ENERGIES
First ionization energy / kJ mol^-1:	597.64
Second ionization energy / kJ mol^-1:	-
Third ionization energy / kJ mol^-1:	-

ABUNDANCE OF ELEMENT
in the atmosphere / ppm:	-
in the Earth's crust / ppm:	0.91
in the oceans / ppm:	0.003

CRYSTALLOGRAPHIC DATA
Crystal structure:	base-centered orthorhombic
Unit-cell dimensions / pm:	a=284.785, b=585.801, c=494.553
Space group:	Cmcm

ISOTOPES
Isotope	Relative atomic mass	Mass percent (%)
²³³U	234.040946(2)	*
²³⁴U	234.040 95(2)	0.0055(5)
²³⁵U	235.043 93(2)	0.7200(12)
²³⁶U	236.045 57(2)	*
²³⁸U	238.050 79(2)	99.2745(60)

REDUCTION POTENTIALS
Balanced half-reaction	E^o / V
U⁴⁺ + e^- → U³⁺	- 0.607
U³⁺ + 3e^- → U(s)	- 1.798
UO₂²⁺ + e^- → UO₂⁺	+0.052
UO₂²⁺ + 3H⁺ + 2e^- → UOH³⁺ + H₂O	+0.299
UO₂²⁺ + 4H⁺ + 2e^- → U⁴⁺ + 2H₂O	+0.334
UO₂²⁺ + 2e^- → UO₂(s)	+0.45
UO₂⁺ + 3H⁺ + e^- → UOH³⁺ + H₂O	+0.546
UO₂⁺ + 4H⁺ + e^- → U⁴⁺ + 2H₂O	+0.612
UOH³⁺ + H⁺ + e^- → U³⁺ + H₂O	- 0.538
UO₂(s) + 4H⁺ + 4e^- → U(s) + 2H₂O	- 1.444
UO₂(s) + 2H₂O + 4e^- → U(s) + 4OH^-	- 2.39
U₃O₈(s) + 4H⁺ + 4e^- → 3UO₂ + 2H₂O	+0.260
U(OH)₃(s) + 3e^- → U(s) + 3OH^-	- 2.17