ActinideElement 94 · f-block

Plutonium (Pu)

Plutonium (Pu) is an actinide with atomic number 94; its most stable known isotope has mass number 244. At room temperature it is a solid that melts at 640 °C and boils at 3,228 °C.

94PuPlutonium[244]

Atomic number

protons

Atomic weight

[244]

most stable isotope

Melting point

640 °C

913.15 K

Boiling point

3,228 °C

3,501.15 K

Density

19.7 g/cm³

near room temperature

Electronegativity

1.28

Pauling scale

State at 25 °C

Solid

Discovered

1940–1941

United States (Berkeley)

Plutonium at a glance

Identity

Symbol	Pu
Atomic number (Z)	94
Atomic weight	[244] mass number of the most stable isotope
Category	Actinide
Group	— (f-block: actinide series)
Period	7
Block	f-block
CAS number	7440-07-5

Atomic properties

Electron configuration	[Rn] 5f⁶ 7s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁶ 6s² 6p⁶ 7s²
Electrons per shell	2, 8, 18, 32, 24, 8, 2
Oxidation states	+4 Less common: +2, +3, +5, +6, +7, +8
Electronegativity (Pauling)	1.28
First ionisation energy	6.026 eV (581.4 kJ/mol) 2nd: 11.5 eV · 3rd: 21.1 eV
Atomic radius (empirical)	175 pm
Covalent radius	172 pm
Van der Waals radius	243 pm

Physical properties

State at 25 °C	Solid
Melting point	640 °C · 1,184 °F · 913.15 K
Boiling point	3,228 °C · 5,842.4 °F · 3,501.15 K
Density	19.7 g/cm³
Crystal structure	Monoclinic

Isotopes & abundance

Natural occurrence	Synthetic (traces in uranium ores)
Radioactive	Yes
Most stable isotope	²⁴⁴Pu — half-life 81.3 million years
Known isotopes	27

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Plutonium electron configuration

Plutonium has 94 electrons. Written in short form, its ground-state configuration is [Rn] 5f⁶ 7s² — the electrons of the noble gas radon, plus 5f⁶ 7s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁶ 6s² 6p⁶ 7s².

5f↑↑↑↑↑↑

7s↑↓

Discovery and name

Discovered

1940–1941 — Glenn T. Seaborg, Arthur Wahl, Joseph W. Kennedy and Edwin McMillan · United States (Berkeley).

Name

The dwarf planet Pluto.

Known for

Plutonium-239 is used in nuclear weapons and MOX reactor fuel; plutonium-238 powers spacecraft such as Voyager and the Mars rovers.

Isotopes of plutonium

Plutonium has no stable isotopes and does not occur naturally in significant amounts. Its longest-lived known isotope is:

Isotope	Protons	Neutrons	Half-life
²⁴⁴Pu	94	150	81.3 million years

27 isotopes of plutonium are known in our data set (half-lives as published in nuclear data tables).

Plutonium and its neighbours in the actinide series

Neighbouring elements in the same f-block series:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Protactinium	91	231.04	1,572 °C	—	15.4 g/cm³	1.5
Uranium	92	238.03	1,135 °C	4,131 °C	19.1 g/cm³	1.38
Neptunium	93	[237]	644 °C	—	20.2 g/cm³	1.36
Plutonium	94	[244]	640 °C	3,228 °C	19.7 g/cm³	1.28
Americium	95	[243]	1,176 °C	—	12 g/cm³	1.3
Curium	96	[247]	1,345 °C	—	13.51 g/cm³	1.3
Berkelium	97	[247]	986 °C	—	14.78 g/cm³	1.3

Frequently asked questions

6 answers

What is the atomic mass of plutonium?

Plutonium has no stable isotopes, so it has no standard atomic weight. Periodic tables show [244], the mass number of its most stable known isotope.

How many protons, neutrons and electrons does plutonium have?

A neutral plutonium atom has 94 protons and 94 electrons. Its most stable isotope, plutonium-244, has 150 neutrons.

What is the electron configuration of plutonium?

[Rn] 5f⁶ 7s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁶ 6s² 6p⁶ 7s²).

What are the melting and boiling points of plutonium?

Plutonium melts at 640 °C (1,184 °F) and boils at 3,228 °C (5,842.4 °F).

Is plutonium a metal?

Plutonium is a metal. It is in the f-block, period 7, and is a solid at room temperature.

Who discovered plutonium?

1940–1941 — Glenn T. Seaborg, Arthur Wahl, Joseph W. Kennedy and Edwin McMillan (United States (Berkeley)).