Plutonium
Atomic Data
| Atomic Number | 94 |
| Symbol | Pu |
| Atomic Weight | 244 u |
| Density (STP) | 19.84 g/cm³ |
| Melting Point | 639.35 °C (912.5 K) |
| Boiling Point | 3231.85 °C (3505 K) |
| Electronegativity | 1.28 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f6 6s2 6p6 7s2 |
| Oxidation States | +3, +4, +5, +6 |
| Phase at STP | Solid |
| Category | Actinoid |
| Period / Group | 7 / None |
| CAS Number | 7440-07-5 |
Electron Configuration
[Rn] 5f6 7s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| O | 5 | 5f | 6 | 84 |
| P | 6 | 6s | 2 | 86 |
| P | 6 | 6p | 6 | 92 |
| Q | 7 | 7s | 2 | 94 |
| Total | 94 | 94 | ||
Isotopes of Plutonium
Plutonium has four naturally occurring stable isotopes. The most abundant is ²³⁸Pu, comprising None% of all naturally occurring Plutonium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Plutonium-238 | ²³⁸Pu | 94 | 144 | trace | Stable |
| Plutonium-239 | ²³⁹Pu | 94 | 145 | trace | Stable |
| Plutonium-240 | ²⁴⁰Pu | 94 | 146 | trace | Stable |
| Plutonium-244 | ²⁴⁴Pu | 94 | 150 | trace | Stable |
Abundance & Occurrence
Plutonium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Alpha radiation: high radiotoxicity: Plutonium-239 (t½ = 24,100 years, alpha emitter) is one of the most radiotoxic substances known when inhaled; microgram quantities of Pu-239 deposited in the lung carry a significant lifetime lung cancer risk.
- Criticality hazard: Pu-239 is fissile; accumulation of approximately 10 kg in close geometry can sustain an uncontrolled chain reaction (criticality); strict mass, shape, and moderation controls are mandatory in any licensed plutonium facility.
- Chemical toxicity: Plutonium is a heavy metal toxin affecting the liver and kidneys in addition to its radiological hazard; plutonium compounds must be handled in negative-pressure glove boxes with continuous air monitoring.
- Fire hazard: Plutonium metal powder is pyrophoric; metal fires generate plutonium oxide aerosols that create severe internal contamination hazards: fire prevention is a primary safety priority in Pu facilities.
- Regulatory controls: Plutonium is tightly controlled under international safeguards; its possession, production, and transfer require licensing and IAEA oversight.
Plutonium in the Real World
Real-World Uses
- Nuclear reactor fuel (MOX): Mixed oxide fuel (MOX), consisting of plutonium dioxide blended with depleted uranium dioxide, is used in light-water reactors to consume surplus weapons-grade plutonium and to extend uranium fuel resources.
- Nuclear weapons: Plutonium-239 is the primary fissile material in modern nuclear weapons; the Fat Man bomb dropped on Nagasaki in 1945 used a Pu-239 implosion design.
- Radioisotope thermoelectric generators (RTGs): Plutonium-238 (t½ = 87.7 yr) decays with intense heat generation; Pu-238 oxide pellets power RTGs in deep-space probes (Voyager 1 and 2, Cassini, New Horizons) and the Curiosity and Perseverance Mars rovers, providing electricity where solar panels are impractical.
- Cardiac pacemaker power sources (historical): Pu-238 RTGs were used in nuclear-powered cardiac pacemakers implanted in thousands of patients in the 1970s; they have been superseded by long-life lithium batteries, but remain active in many still-living patients.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is plutonium used for?
Plutonium-239 is a key fissile material in nuclear weapons: it is the core of the implosion-type atomic bomb (the Fat Man design). Plutonium-239 is also used as nuclear fuel in some reactors. Plutonium-238, with its steady heat output from alpha decay, is used in radioisotope thermoelectric generators (RTGs) that power deep space probes including Voyager, Cassini, New Horizons, and the Mars Curiosity and Perseverance rovers.
Is plutonium the most dangerous element?
Plutonium's danger depends on form and dose. Its main radiological hazard is as an alpha emitter: if plutonium particles are inhaled, they lodge in lung tissue and deliver continuous alpha radiation with a very long effective biological half-life, causing lung cancer. Plutonium-239 also accumulates in liver and bone. As a nuclear weapon material it poses catastrophic potential hazards. Its chemical toxicity is comparable to other heavy metals. The myth that a speck is instantly lethal is an exaggeration, but plutonium is genuinely among the most hazardous substances known when inhaled.
How was plutonium discovered?
Plutonium was synthesised in December 1940 and identified in early 1941 by Glenn Seaborg, Arthur Wahl, Joseph Kennedy, and Edwin McMillan at Berkeley. They bombarded uranium-238 with deuterons in a cyclotron, producing neptunium-238, which then decayed to plutonium-238. They subsequently identified plutonium-239 as fissile. Seaborg named it plutonium after Pluto, then considered the outermost planet (following the neptunium–Neptune naming). Seaborg received the 1951 Nobel Prize in Chemistry.
How does a plutonium RTG power a space probe?
Plutonium-238 decays by alpha emission with a half-life of 87.7 years, generating a consistent amount of heat. In a radioisotope thermoelectric generator (RTG), this heat flows through thermocouples that convert a temperature difference directly into electricity with no moving parts. The Voyager 1 probe, launched in 1977, still operates today on its Pu-238 RTGs, now over 45 years into its mission and beyond the edge of the solar system.