Plutonium (Pu)
Element 94 · Actinide · atomic mass [244] u · f-block, period 7
Electron shells: 2, 8, 18, 32, 24, 8, 2
Plutonium is warm to the touch from its own radioactive decay and is one of the most tightly controlled substances on Earth. Its 238 isotope has powered deep-space probes for decades.
Voyager 1 has been running on plutonium-238 heat since 1977 and is still transmitting.
- Atomic number
- 94
- Atomic mass
- [244] u
- Electron configuration
- [Rn] 7s² 5f⁶
- Group · period · block
- f-block · 7 · f
- Oxidation states
- +3, +4, +5, +6
- Electronegativity
- 1.28 (Pauling)
- Melting point
- 640 °C
- Boiling point
- 3,228 °C
- Density
- 19.84 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-white metal, tarnishes yellow
- Discovered
- Glenn T. Seaborg and colleagues, 1940
94 protons, and 94 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Shown in the strip below the table
What Plutonium is used for
- Nuclear weapons
- Radioisotope generators for spacecraft
- Reactor fuel (MOX)
Atomic structure of Plutonium
A neutral plutonium atom has 94 protons and 94 electrons. Its most common isotope carries about 150 neutrons, which is where the mass number 244 comes from. Change the neutron count and you have a different isotope of plutonium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 24, 8, 2. In orbital notation that is [Rn] 7s² 5f⁶. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Plutonium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Plutonium sits in the periodic table
Discovery and naming
Plutonium was discovered by Glenn T. Seaborg and colleagues in 1940. Its name comes from The dwarf planet Pluto, which is also why its symbol (Pu) does not match its English name.
Every isotope of plutonium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Plutonium?
Plutonium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 244 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Plutonium have?
Plutonium has 94 protons, because the atomic number is the proton count and that is what makes an atom Plutonium at all. A neutral Plutonium atom has the same number of electrons, 94. The neutron count varies by isotope; the most common one has about 150, since 244 − 94 = 150.
What is the electron configuration of Plutonium?
The electron configuration of Plutonium is [Rn] 7s² 5f⁶. Its electrons are arranged 2, 8, 18, 32, 24, 8, 2 across 7 shells.
Is Plutonium a metal?
Yes. Plutonium is classified as a actinide, on the metallic side of the table.
What group and period is Plutonium in?
Plutonium sits in the f-block strip below the main table, in period 7, among the actinides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Plutonium?
Plutonium most commonly forms a 4+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound. Across all its compounds it shows oxidation states of +3, +4, +5, +6.
What is the melting point of Plutonium?
Plutonium melts at 640 °C and boils at 3,228 °C. That puts it in the solids at everyday temperatures.
What is Plutonium used for?
Nuclear weapons, Radioisotope generators for spacecraft, Reactor fuel (MOX). Plutonium is warm to the touch from its own radioactive decay and is one of the most tightly controlled substances on Earth.
Who discovered Plutonium, and where does its name come from?
Plutonium (Pu) was discovered by Glenn T. Seaborg and colleagues in 1940. The name comes from The dwarf planet Pluto.
Is Plutonium radioactive?
Yes. Every isotope of Plutonium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.