Plutonium ($Pu$)
The heavy, synthetic powerhouse—a radioactive actinide that changed the trajectory of the 20th century and powers the missions of deep space exploration.
Plutonium is the most famous transuranic element. It was first synthesized in 1940 by a team lead by Glenn T. Seaborg, Edwin McMillan, Joseph W. Kennedy, and Arthur C. Wahl at the Berkeley Radiation Laboratory. They created it by bombarding uranium-238 with deuterons, creating neptunium-238 which then decayed into plutonium-238. They named the element after Pluto, continuing the tradition set by the names of Uranus (Uranium) and Neptune (Neptunium).
As a member of the actinide series, plutonium is a heavy, silvery-white metal. It is highly radioactive and exists in several allotropic forms, each with different densities and crystal structures. Because its most stable isotope, plutonium-239, has a half-life of 24,100 years, it persists in the environment for millennia, making its management one of the great challenges of modern nuclear science.
Atomic & Physical Properties
Plutonium is a dense metal that exhibits complex physical behavior. It is one of the few elements that changes density and volume significantly as it transforms between its various allotropes.
| Property | Value |
|---|---|
| Atomic Number | 94 |
| Standard Atomic Weight | [244] |
| Electron Configuration | $[Rn] 5f^6 7s^2$ |
| Most Stable Isotope | 244Pu (Half-life: 80 million years) |
| Common Oxidation States | +3, +4, +5, +6 |
| Melting Point | 913 K (640 °C) |
| Density | 19.86 g/cm³ |
Fissile Power: Plutonium-239
Plutonium-239 is the primary isotope used in nuclear reactors and weapons. It is fissile, meaning its nucleus can capture a slow neutron and immediately undergo nuclear fission, releasing a massive amount of energy and several more neutrons to sustain a chain reaction.
This isotope is produced in nuclear reactors by the neutron bombardment of U-238, a process that has made plutonium a central element in discussions of nuclear proliferation and energy strategy.
Chemical Reactivity
Plutonium is highly reactive. Like other actinides, it is electropositive and reacts readily with oxygen, halogens, and acids.
Reaction with Air
Plutonium oxidizes in air to form a surface layer of Plutonium Dioxide ($PuO_2$). In finely divided form, it is pyrophoric and can ignite spontaneously.
Radiation Safety
Plutonium is a potent alpha-emitter and an internal radiation hazard. Its primary risk to humans is not external (as alpha particles are blocked by skin), but internal: if dust is inhaled, it lodges in the lungs or skeleton, where it can cause long-term cellular damage and cancer.
Powering the Future: RTGs
Plutonium-238 is the heartbeat of deep-space exploration. It produces heat through alpha decay, which is converted into electricity by Radioisotope Thermoelectric Generators (RTGs). RTGs have powered famous missions like Voyager 1 & 2, Cassini, and the Perseverance Mars rover, providing reliable, long-term power in the dark, cold vacuum of space.
This is the ninety-fourth part of our "Elements and Their Properties" series. We are deep into the actinide frontier! To master the mechanics of nuclear physics and the chemistry of heavy elements, visit our Success Blueprint.
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