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Wednesday, February 9, 2011

Plutonium (Worlds Most Dangerous Element )

             Plutonium is a 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.
Plutonium is the heaviest primordial element, by virtue of its most stable isotope, plutonium-244, whose half-life of about 80 million years is just long enough for the element to be found in trace quantities in nature.
The most important isotope of plutonium is plutonium-239, with a half-life of 24,100 years. Plutonium-239 is the isotope most useful for nuclear weapons. 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. These can therefore sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors.
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 neutron flux of any sample it is in. The presence of plutonium-240 limits a sample's usability for weapons or reactor fuel, and determines its grade.

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