Atomic Number: 94
Atomic Weight: 244.0642
Discovery: G.T. Seaborg, J.W. Kennedy, E.M. McMillan, A.C. Wohl (1940, United States)
Electron Configuration: [Rn] 5f6 7s2
Word Origin: Named for the planet Pluto.
Isotopes: There are 15 known isotopes of plutonium. The isotope of greatest importance is Pu-239, with a half-life of 24,360 years.
Properties: Plutonium has a specific gravity of 19.84 (a modification) at 25°C, melting point of 641°C, boiling point of 3232°C, with a valence of 3, 4, 5, or 6. Six allotropic modifications exist, with various crystalline structures and densities ranging from 16.00 to 19.86 g/cm3. The metal has a silvery appearance which takes a yellow cast when oxidized slightly. Plutonium is a chemically reactive metal. It readily dissolves in concentrated hydrochloric acid, perchloric acid, or hydroiodic acid, forming the Pu3+ ion. Plutonium exhibits four ionic valence states in ionic solution. The metal has the nuclear property of being readily fissionable with neutrons. A relatively large piece of plutonium gives off enough energy via alpha decay to be warm to the touch. Larger pieces of plutonium give off sufficient heat to boil water. Plutonium is a radiological poison and must be handled with care. It is also important to take precautions to prevent the unintentional formation of critical mass. Plutonium is more likely to become critical in liquid solution than as a solid. The shape of the mass is an important factor for criticality.
Uses: Plutonium is used as an explosive in nuclear weapons. The complete detonation of a kilogram of plutonium produces an explosion equal to that produced by approximately 20,000 tons of chemical explosive. One kilogram of plutonium is equivalent to 22 million kilowatt hours of heat energy, so plutonium is important for nuclear power.
Sources: Plutonium was the second transuranium actinide to be discovered. Pu-238 was produced by Seaborg, McMillan, Kennedy, and Wahl in 1940 by deuteron bombardment of uranium. Plutonium may be found in trace amount in natural uranium ores. This plutonium is formed by irradiation of natural uranium by the neutrons which are present. Plutonium metal can be prepared by reduction of its trifluoride with alkaline earth metals.
Element Classification: Radioactive Rare Earth (Actinide)
Density (g/cc): 19.84
Melting Point (K): 914
Boiling Point (K): 3505
Appearance: silvery-white, radioactive metal
Atomic Radius (pm): 151
Ionic Radius: 93 (+4e) 108 (+3e)
Fusion Heat (kJ/mol): 2.8
Evaporation Heat (kJ/mol): 343.5
Pauling Negativity Number: 1.28
First Ionizing Energy (kJ/mol): 491.9
Oxidation States: 6, 5, 4, 3
Lattice Structure: Monoclinic
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)