Uranium Element Facts

238.029
Uranium

Uranium ore (left) and uranium oxides in sample tubes. These oxides, known as yellowcake, are formed during the purification of uranium ores.

General:

Name: Uranium	Symbol: U
Type: Rare Earth, Actinides	Atomic weight: 238.029
Density @ 293 K: 18.9 g/cm³	Atomic volume: 12.59 cm³/mol
Discovered: In ancient times uranium oxide was used to produce yellow colored ceramic glazes. Uranium was formally discovered in 1789 by Martin Heinrich Klaproth. Klaproth was studying the mineral pitchblende, which was then believed to be a zinc/iron ore. Klaproth dissolved pitchblende in nitric acid, then added potash (potassium carbonate) to obtain a yellow precipitate. Adding excess potash dissolved the yellow precipitate. Such reactions were not characteristic of any known element and Klaproth concluded he had discovered a new element. ⁽¹⁾ He named it after the recently discovered planet Uranus. In 1841, Eugene-Melchior Peligot isolated uranium metal by heating uranium tetrachloride with potassium.

States

State (s, l, g): solid
Melting point: 1408 K (1135 ^oC)	Boiling point: 4403 K (4130 ^oC)

Energies

Specific heat capacity: 0.12 J g^-1 K^-1	Heat of atomization: 482 kJ mol^-1
Heat of fusion: 8.520 kJ mol^-1	Heat of vaporization : 422.58 kJ mol^-1
1^st ionization energy: 597.6 kJ mol^-1	2^nd ionization energy: 1420 kJ mol^-1
3^rd ionization energy: kJ mol^-1	Electron affinity: kJ mol^-1

Oxidation & Electrons

Shells: 2,8,18,32,21,9,2	Electron configuration: [Rn] 5f³ 6d¹ 7s²
Minimum oxidation number: 0	Maximum oxidation number: 6
Min. common oxidation no.: 0	Max. common oxidation no.: 6
Electronegativity (Pauling Scale):	Polarizability volume: 27.4 Å³

Appearance & Characteristics

Structure: orthorhombic	Color: silvery-white
Hardness: 6.0 mohs
A look at uranium and its compounds. The former gas diffusion plant at Oak Ridge, conveying the scale of facilities needed to process fissile uranium. A neutron collides with a U-235 atom. U-236 forms briefly before it undergoes nuclear fission; this yields new atoms plus energy plus more neutrons. These newly released neutrons can cause more U-235 to split. If U-235 atoms are present in high enough concentrations, a nuclear chain reaction results.	Harmful effects: Uranium is harmful both through its chemical toxicity and its radioactivity. Exposure to uranium increases your risk of getting a variety of cancers due to its radioactivity. Characteristics: Uranium is a dense, silvery-white, slightly paramagnetic, radioactive metal. It is also ductile and malleable. The metal tarnishes in air acquiring a dark layer of oxide. When finely powdered, uranium ignites spontaneously in air. Uranium is a highly reactive metal and reacts with almost of all the nonmetallic elements and many of their compounds. It dissolves in acids, but it is insoluble in alkalis. All isotopes of uranium are radioactive, some more so than others. Its radioactivity - in particular its capacity to undergo thermonuclear chain reactions - has led to uranium's use in energy generation, both for civilian and military purposes. Uses: Uranium is used as fuel for nuclear power plants. One kilogram of uranium-235 has the capacity to produce as much energy as 1,500,000 kilograms (1,500 tonnes) of coal. Naturally occurring uranium is over 99% U-238 with only about 0.7% of the fissile U-235. Huge gas diffusion plants are used to produce enriched uranium, which has higher concentrations of U-235. Uranium for use in nuclear power plants is enriched to a U-235 concentration of 2-3%. In nuclear weapons, it is believed uranium is enriched to about 90% U-235, although lower concentrations would still yield a working bomb. Depleted uranium is a byproduct of enriching uranium for nuclear purposes. It contains only about 0.2% U-235 and is only a little over half as radioactive as naturally occurring uranium. Its lower radioactivity has allowed depleted uranium to be used in applications where uranium's very high density is useful. (A tennis ball sized sphere of uranium would weigh about 5.7 pounds (2.6 kilograms).) It is used by the military as shielding to protect army tanks, and also in parts of bullets and missiles. Use of depleted uranium in missiles is controversial because, on impact, uranium vapor and dust form and these are highly toxic. U-238 can be converted into fissionable plutonium in breeder reactors.

Reactions

Reaction with air: mild, ⇒ U₃O₈	Reaction with 6 M HCl: mild, ⇒ H₂
Reaction with 15 M HNO₃: passivated	Reaction with 6 M NaOH: mild, ⇒ none

Compounds

Oxide(s): UO, UO₂, UO₃ , U₂O₅, U₃O₈,	Chloride(s): UCl, UCl₃, UCl₄, UCl₅, UCl₆
Hydride(s): UH₃

Radius

Atomic radius: 175 pm	Ionic radius (1+ ion): pm
Ionic radius (2+ ion): pm	Ionic radius (3+ ion): 116.5 pm
Ionic radius (2- ion): pm	Ionic radius (1- ion): pm

Conductivity

Thermal conductivity: 27.5 W m^-1 K^-1

Electrical conductivity: 3.6 x 10^-6 S m^-1

Abundance & Isotopes

Abundance earth's crust: 2.7 parts per million by weight, 0.25 parts per million by moles
Abundance solar system: 1 part per billion by weight, 4 parts per trillion by moles
Cost, pure: $ per 100g
Cost, bulk: $11 per 100g
Source: Uranium occurs naturally in several minerals such as uraninite (uranium oxide), carnotite and autunite. Canada is the world's largest supplier of uranium, producing 20 to 30 percent of supplies. ⁽²⁾ Commercially, uranium is produced through the reduction of uranium halides with alkali earth metals. Although most people think uranium is extraordinarily rare, it is in fact more abundant than familiar elements such as mercury and silver.
Isotopes: Uranium has 21 isotopes whose half-lives are known, with mass numbers 218 to 242. Natural uranium consists of three major isotopes: ²³⁴U, ²³⁵U, and ²³⁸U. All are radioactive. ²³⁸U is the most stable isotope, with a half-life of 4.51 x 10⁹ years (almost the age of the Earth).

References

1. Mary Elvira Weeks, Discovery of the Elements., (2003) p56. Kessinger Publishing Co.
2. Uranium Canada

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