Plutonium

neptunium ← plutonium → americium Sm ↑ Pu ↓ —

Atomic properties Atomic number 94 Electron configuration [Rn] 5f6 7s2 Physical properties Melting point 640 °C (913 K) Boiling point 3230 °C (3500 K) Density 19.86 g cm−3 Electric resistivity 146 × 10−6 Ω cm Chemical properties Electronegativity 1.28 (Pauling) Ionization energy 6.0258(2) eV, 581.40(2) kJ mol−1 Atomic radii Covalent radius 187 pm Metallic radius 159 pm Ionic radius 85 pm (Pu6+, Oh) 100 pm (Pu4+, Oh) Thermodynamic properties Standard entropy 50.5 J K−1 mol−1 Enthalpy change of fusion 5.19 kJ mol−1 Enthalpy change of vaporization 394(25) kJ mol−1 Molar heat capacity (Cp) 29.6 J K−1 mol−1 Miscellaneous CAS number 7440-07-5 EC number 231-117-7 Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).

Plutonium (symbol: Pu) is a chemical element, a member of the actinoid series. All isotopes of plutonium are unstable, with half-lives of less than 81 million years: any plutonium that was present at the formation of the Solar System has long since decayed, although trace amounts of plutonium are naturally formed by the capture of neutrons by uranium-238. Apart from these traces, plutonium is prepared artificially in nuclear reactors: about 2000 tonnes of plutonium has been prepared in this way.

Plutonium was first prepared in 1940 by Glenn Seaborg and Edwin McMillan at the University of California Radiation Laboratory, by the deuteron bombardment of uranium-238. It was named after the planet Pluto, by analogy with uranium, named after the planet Uranus, and neptunium, named after the planet Neptune.

Notes and references

Further reading

• Lemire, R. J.; Fuger, J.; Nitsche, H.; Potter, P.; Rand, M. H.; Rydberg, J.; Spahiu, K.; Sullivan, J. C., et al. Chemical Thermodynamics of Neptunium and Plutonium; Elsevier: Amsterdam, 2001. ISBN 044450379X.

External links

• WebElements