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(
94PuPeriodic table
Appearance
silvery white
General properties
Name, symbol, number plutonium, Pu, 94
Element category actinide
Group, period, block n/a, 7, f
Standard atomic weight (244) g·mol−1
Electron configuration [Rn] 5f6 7s2
Electrons per shell 2, 8, 18, 32, 24, 8, 2 (Image)
Physical properties
Phase solid
Density (near r.t.) 19.816 g·cm−3
Liquid density at m.p. 16.63 g·cm−3
Melting point 912.5 K, 639.4 °C, 1182.9 °F
Boiling point 3505 K, 3228 °C, 5842 °F
Heat of fusion 2.82 kJ·mol−1
Heat of vaporization 333.5 kJ·mol−1
Specific heat capacity (25 °C) 35.5 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1756 1953 2198 2511 2926 3499
Atomic properties
Oxidation states 7, 6, 5, 4, 3
(amphoteric oxide)
Electronegativity 1.28 (Pauling scale)
Ionization energies 1st: 584.7 kJ·mol−1
Atomic radius 159 pm
Covalent radius 187±1 pm
Miscellanea
Crystal structure monoclinic
Magnetic ordering paramagnetic[1]
Electrical resistivity (0 °C) 1.460 µΩ·m
Thermal conductivity (300 K) 6.74 W·m−1·K−1
Thermal expansion (25 °C) 46.7 µm·m−1·K−1
Speed of sound 2260 m/s
Young's modulus 96 GPa
Shear modulus 43 GPa
Poisson ratio 0.21
CAS registry number 7440-07-5
Most stable isotopes
Main article: Isotopes of plutonium
iso NA half-life DM DE (MeV) DP
238Pu syn 88 y SF 204.66[2] —
α 5.5 234U
239Pu trace 2.41 × 104 y SF 207.06 —
α 5.157 235U
240Pu syn 6.5 × 103 y SF 205.66 —
α 5.256 236U
241Pu syn 14 y β− 0.02078 241Am
SF 210.83 —
242Pu syn 3.73 × 105 y SF 209.47 —
α 4.984 238U
244Pu trace 8.08 × 107 y α 4.666 240U
SF —
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Plutonium (pronounced /pluːˈtoʊniəm/ ploo-TOE-nee-əm) is a rare transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-white appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen and silicon. When exposed to moist air, it forms oxides and hydrides that expand the sample up to 70% in volume, which in turn flake off as a powder that can spontaneously ignite. It is also a radioactive poison that accumulates in bone marrow. These and other properties make the handling of plutonium dangerous.
The most important isotope of plutonium is plutonium-239, with a half-life of 24,100 years. Plutonium-239 and 241 are fissile, meaning the nuclei of their atoms can break apart by being bombarded by slow moving thermal neutrons, releasing energy, gamma radiation and more neutrons. It can therefore sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. Plutonium is the heaviest naturally-occurring or primordial element; the most stable isotope of plutonium is plutonium-244, with a half-life of about 80 million years, long enough to be found in trace quantities in nature.[3] Plutonium-238 has a half-life of 88 years and emits alpha particles. It is a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft. Plutonium-240 has a high rate of spontaneous fission, raising the background neutron rate of any sample it is contained in. The presence of plutonium-240 effectively limits a sample's weapon and power potential and determines its grade: weapons (< 7%), fuel (7–19%) and reactor grade (> 19%).
Element 94 was first synthesized in 1940 by a team led by Glenn T. Seaborg and Edwin McMillan at the University of California, Berkeley laboratory by bombarding uranium-238 with deuterons. McMillan named the new element after Pluto, and Seaborg suggested the symbol Pu as a joke. Trace amounts of plutonium were subsequently discovered in nature. Discovery of plutonium became a classified part of the Manhattan Project to develop an atomic bomb during World War II. The first nuclear test, "Trinity" (July 1945), and the second atomic bomb used to destroy a city (Nagasaki, Japan, in August 1945), "Fat Man", both had cores of plutonium-239. Human radiation experiments studying plutonium were conducted without informed consent, and a number of criticality accidents, some lethal, occurred during and after the war. Disposal of plutonium waste from nuclear power plants and dismantled nuclear weapons built during the Cold War is a major nuclear-proliferation, health, and environmental concern. Other sources of plutonium in the environment are fallout from numerous above-ground nuclear tests (now banned) and several nuclear accidents.
