Plutonium Facts (Pu or Atomic Number 94)

Plutonium Chemical and Physical Properties

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Plutonium is element atomic number 94 with element symbol Pu. It is a radioactive metal in the actinide series. Pure plutonium metal is silvery-gray in appearance, but it glows red in the dark because it is pyrophoric. This is a collection of plutonium element facts.

Plutonium Basic Facts

Atomic Number: 94

Symbol: Pu

Atomic Weight: 244.0642

Discovery: G.T. Seaborg, J.W. Kennedy, E.M. McMillan, A.C. Wohl (1940, United States). The first sample of plutonium was produced by deuteron bombardment of uranium in a cyclotron at the University of California at Berkeley. The reaction produced neptunium-238, which decayed via beta emission to form plutonium. While the discovery was documented in a paper sent to Physical Review in 1941, the announcement of the element was delayed until after World War II ended. This was because plutonium was predicted to be fissile and relatively easy to produce and purify using a slow nuclear reactor fueled with uranium to produce plutonium-239.

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.

Toxicity: Even if it wasn't radioactive, plutonium would be toxic as a heavy metal. Plutonium accumulates in bone marrow. As the element decays, it release alpha, beta, and gamma radiation. Both acute and long-term exposure may result in radiation sickness, cancer, and death. Inhaled particles can cause lung cancer. Ingested particles primarily damage the liver and skeleton. Plutonium serves no known biological role in any organism.

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)

Plutonium Physical Data

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


  • Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford University Press. ISBN 978-0-19-960563-7.
  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  • Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 978-0-8493-0485-9.
  • Seaborg, Glenn T. The Plutonium Story. Lawrence Berkeley Laboratory, University of California. LBL-13492, DE82 004551.
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 0-8493-0464-4.
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Helmenstine, Anne Marie, Ph.D. "Plutonium Facts (Pu or Atomic Number 94)." ThoughtCo, Feb. 16, 2021, Helmenstine, Anne Marie, Ph.D. (2021, February 16). Plutonium Facts (Pu or Atomic Number 94). Retrieved from Helmenstine, Anne Marie, Ph.D. "Plutonium Facts (Pu or Atomic Number 94)." ThoughtCo. (accessed June 5, 2023).