Fermium

Found in the same hydrogen bomb debris as einsteinium, and named for Enrico Fermi, who built the first nuclear reactor.

At a glance

Symbol: Fm
Atomic number: 100
Mass number of its longest-lived isotope: [257]
Group: none; it sits in the actinide row below the table
Period: 7
Family: actinide
Electron configuration: [Rn] 5f¹² 7s²
Electronegativity: 1.30
Common ions: Fm³⁺
Isotopes: none are stable; ²⁵⁷Fm lasts longest, about 100 days

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: never made in visible amounts; expected to be a metal
Melting point: 1527 °C (predicted)
Boiling point: not known
Density: not measured

Where it is found

Not found in nature; made in trace amounts in high-flux reactors.

Discovery and name

Albert Ghiorso's team found it in 1952 in debris from the Ivy Mike hydrogen bomb test, alongside einsteinium, and it was named in 1955 after Enrico Fermi. It is the heaviest element that can be made by bombarding lighter elements with neutrons; everything heavier needs a particle accelerator.

What it is used for

Research only.

Handle with care

Radioactive; only trace amounts have ever been made.