What Is Plutonium?
Plutonium is a chemical element with the symbol Pu and atomic number 94, part of the radioactive actinide series.
A radioactive actinide used in nuclear weapons and as fuel in spacecraft.
As a actinide in Period 7 and Group 3 (Transition Metals), plutonium's placement on the table reflects its electron configuration of [Rn] 5f⁶ 7s², which governs its bonding behavior and the type of compounds it typically forms.
Position on the Periodic Table
Plutonium is located in Period 7, the bottom row of the standard periodic table, consisting largely of radioactive and synthetic elements.
Within that row, plutonium sits in Group 3 (Transition Metals), alongside elements that share a similar number of valence electrons and, by extension, similar chemical behavior.
This position is not arbitrary — the periodic table was deliberately organized so that an element's row and column reveal its expected reactivity, bonding pattern, and physical state at a glance.
Physical & Chemical Properties
Plutonium has an atomic mass of (244) u and a density of 19.84 g/cm³. Its melting point is 640°C and its boiling point is 3228°C.
Plutonium is radioactive, like every other member of the actinide series, with a nucleus prone to spontaneous decay.
Electron Configuration Explained
Plutonium's electron configuration is [Rn] 5f⁶ 7s², describing how its electrons are distributed across shells and subshells around the nucleus.
Reading the configuration in order shows electrons filling shells of increasing energy, following the standard Aufbau principle that explains how atomic structure builds up across the periodic table.
The outermost (valence) electrons shown in this configuration are what ultimately determine plutonium's chemical reactivity and the type of bonds it forms with other elements.
History & Discovery
Plutonium was formally discovered in 1940, G.T. Seaborg, identified through the careful isolation and analytical techniques typical of that era's chemical research.
Many elements from this period were anticipated by Dmitri Mendeleev's periodic table, which successfully predicted gaps corresponding to undiscovered elements well before laboratory instruments existed to confirm them directly.
What Is Plutonium Used For?
Plutonium's specific properties make it useful in several applications, including:
- Nuclear weapons
- Nuclear reactors (MOX fuel)
- Spacecraft power (RTG)
- Research
- Medical tracers
These uses reflect plutonium's underlying classification as a actinide, since the same properties that define its category in chemistry also determine where it becomes practically useful.
Fun Facts About Plutonium
- The Voyager spacecraft are powered by plutonium-238 RTGs — still working after 47+ years.
- Plutonium is element number 94 on the periodic table, in Period 7 and Group 3.
- Its standard atomic mass is (244) u, calculated from the natural abundance of its isotopes.
Frequently Asked Questions
What is Plutonium's atomic number?
Plutonium has atomic number 94.
What is Plutonium's chemical symbol?
Plutonium's symbol is Pu.
What group and period is Plutonium in?
Plutonium is in Period 7, Group 3 (Transition Metals).
What is Plutonium's atomic mass?
Plutonium's standard atomic mass is (244) u.