---
title: "Plutonium (Pu) — element 94"
description: "Plutonium is element 94, symbol Pu, most stable isotope 244. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/plutonium/
site: "At One Place"
---

# Plutonium (Pu)

**Plutonium — element 94: Pu**

[244] · Actinide · period 7

Plutonium has six solid crystal forms between room temperature and its melting point, more than any other element, and they differ in density by as much as 25% — a plutonium casting can crack itself simply by cooling through a phase change, which is why weapons plutonium is alloyed with a little gallium to hold it in one phase. It is a poor conductor of heat and electricity, unusually for a metal, and a lump of it is warm to the touch from its own decay. Voyager 1 and 2 have been running on plutonium-238 since 1977, and both are still transmitting.

## Properties

- **Atomic number:** 94
- **Symbol:** Pu
- **Mass number of most stable isotope:** [244]
- **Category:** Actinide
- **Period:** 7
- **Block:** f-block
- **Electron configuration:** [Rn] 7s² 5f⁶
- **Electrons per shell:** 2, 8, 18, 32, 24, 8, 2
- **Melting point:** 913 K — 639.9 °C — 1183.7 °F
- **Boiling point:** 3,501 K — 3227.8 °C — 5842.1 °F
- **Density:** 19.84 g/cm³
- **Electronegativity:** 1.28 (Pauling)
- **Oxidation states:** +4, +6, +5, +3
- **Discovered:** 1940 by Glenn Seaborg, Edwin McMillan, Joseph Kennedy and Arthur Wahl

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁶
- **Noble gas shorthand:** [Rn] 7s² 5f⁶
- **Shells:** K: 2 · L: 8 · M: 18 · N: 32 · O: 24 · P: 8 · Q: 2

## What it is used for

- Nuclear weapon pits
- Plutonium-238 radioisotope generators powering Voyager, Cassini and Curiosity
- MOX reactor fuel, blending plutonium with uranium
- Historically, plutonium-238 pacemaker batteries

## Hazards

- Alpha emitter that is dangerous mainly when inhaled as fine oxide dust
- Fissile and subject to criticality accidents in the wrong geometry
- Finely divided plutonium is pyrophoric and ignites in air

> No stable isotope; the mass given is the mass number of plutonium-244, the longest-lived at 81 million years. The weapon and reactor isotope is plutonium-239, half-life 24,100 years, and the spacecraft isotope is plutonium-238, half-life 87.7 years.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 92 | Uranium | U | 238.03 |
| 93 | Neptunium | Np | [237] |
| 94 | Plutonium ← | Pu | [244] |
| 95 | Americium | Am | [243] |
| 96 | Curium | Cm | [247] |

## Common questions

### What is the atomic number of plutonium?

94. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for plutonium?

Pu.

### What is the electron configuration of plutonium?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁶, or [Rn] 7s² 5f⁶ in noble-gas shorthand.

### What is the melting point of plutonium?

913 K — 639.9 °C — 1183.7 °F

## Related pages

- [Uranium (U)](https://atoneplace.net/element/uranium/)
- [Neptunium (Np)](https://atoneplace.net/element/neptunium/)
- [Americium (Am)](https://atoneplace.net/element/americium/)
- [Curium (Cm)](https://atoneplace.net/element/curium/)

## Sources

- Official vendor product documentation — At One Place (/about/)