Plutonium

At a glance

Symbol

Pu

Atomic number

94

Mass number of its longest-lived isotope

[244]

Group

none; it sits in the actinide row below the table

Period

7

Family

actinide

Electron configuration

[Rn] 5f⁶ 7s²

Electronegativity

1.28

Common ions

+3, +4, +5 and +6 are all possible in water

Isotopes

none are stable; ²⁴⁴Pu lasts longest, about 80 million years; ²³⁹Pu is used in weapons and reactors, and ²³⁸Pu in power sources

On the table

Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.

Electrons and bonding

Radioactive, like every actinide. It gives up electrons to form positive ions.

Properties

State at 25 °C

solid

What it looks like

silvery metal that tarnishes yellow and then olive green, and feels warm from its own radioactivity

Melting point

640 °C

Boiling point

3228 °C

Density

19.8 g/cm³

Odd fact

the metal has six different solid forms between room temperature and its melting point, more than any other element

Where it is found

Only faint traces exist in nature. It is made in nuclear reactors when uranium-238 absorbs neutrons.

Discovery and name

Glenn Seaborg, Arthur Wahl, Joseph Kennedy and Edwin McMillan made it at Berkeley in 1940 and 1941 by bombarding uranium with deuterons, and it was kept secret during the war. It was named for Pluto, then counted as the planet after Neptune. Seaborg said he picked the symbol Pu as a joke and expected it to be rejected; it was not.