Fermium Element Facts

The chemical element fermium is classed as an actinide metal. It was discovered in 1952 by teams of scientists led by Albert Ghiorso.

Hydrogen bomb test.
Fermium Radioactive

The first hydrogen bomb test 'Mike', which produced the world's first known atoms of fermium in 1952.


Data Zone

Classification: Fermium is an actinide metal
Atomic weight: (257), no stable isotopes
State: solid
Melting point: 1527 oC, 1800 K
Boiling point:
Electrons: 100
Protons: 100
Neutrons in most abundant isotope: 157
Electron shells: 2,8,18,32,30,8,2
Electron configuration: [Rn] 5f12 7s2
Density @ 20oC: 8.84 g/cm3
Show more, including: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities
Atomic volume: 29.1 cm3/mol
Structure: close packed cubic
Specific heat capacity
Heat of fusion
Heat of atomization
Heat of vaporization
1st ionization energy 627 kJ mol-1
2nd ionization energy
3rd ionization energy
Electron affinity
Minimum oxidation number 0
Min. common oxidation no. 0
Maximum oxidation number 3
Max. common oxidation no. 3
Electronegativity (Pauling Scale) 1.3
Polarizability volume 23.8 Å3
Reaction with air
Reaction with 15 M HNO3
Reaction with 6 M HCl
Reaction with 6 M NaOH
Atomic radius
Ionic radius (1+ ion)
Ionic radius (2+ ion)
Ionic radius (3+ ion) 91.1 pm
Ionic radius (1- ion)
Ionic radius (2- ion)
Ionic radius (3- ion)
Thermal conductivity
Electrical conductivity
Freezing/Melting point: 1527 oC, 1800 K

Oak Ridge National Laboratory

Aerial View of the High Flux Isotope Reactor at Oak Ridge National Laboratory where fermium is produced.

Discovery of Fermium

Dr. Doug Stewart

Fermium was the eighth synthetic transuranium element of the actinide series to be discovered.

Fermium-255 (half-life 20.07 hours) was identified in 1952 by teams of scientists from the Lawrence Berkeley National Laboratory, the Argonne National Laboratory and the Los Alamos Scientific Laboratory. The project was led by Albert Ghiorso.

It was discovered unexpectedly along with einsteinium in debris from the first hydrogen bomb test, codenamed ‘Mike’, which took place in the Pacific on October 31 1952. The debris was collected on filter papers attached to drone airplanes that flew through the explosion area. Later, to obtain more material, many hundreds of pounds of coral from the blast area were examined. Fermium was identified by chemical analysis with only about 200 atoms. (1)

The new element was produced by nuclear fission of 17 neutrons with uranium-238 (which then underwent eight beta decays). (2)

The results were not published and kept secret until 1955.

In 1954 researchers from the Nobel Institute of Physics in Stockholm produced fermium-250 by bombarding uranium-238 with oxygen-16 ions.

The element was named after the nuclear physicist Enrico Fermi.

Transuranium elements discovery and experiments. 1963 chemistry educational documentary narrated by Glenn Seaborg, Stanley Thompson and Albert Ghiorso.

Appearance and Characteristics

Harmful effects:

Fermium is harmful due to its radioactivity.


Fermium is a synthetic, highly radioactive metal and has only been produced in miniscule amounts.

Under normal conditions, it behaves in aqueous solution as expected for a trivalent actinide ion.(3)

Fermium metal has not been prepared. (3a)

Uses of Fermium

Fermium is of scientific research interest only.

Abundance and Isotopes

Abundance earth’s crust: nil

Abundance solar system:

Cost, pure: $ per g

Cost, bulk: per 100g

Source: Fermium is a synthetic element and is not found naturally. It is produced in nuclear reactors in miniscule amounts from the neutron bombardment of plutonium by a long series of neutron capture reactions.(2)

Isotopes: Fermium has 18 isotopes whose half-lives are known, with mass numbers 242 to 259. Fermium has no naturally occurring isotopes. Its longest lived isotopes are 257Fm, with a half-life of 100.5 days, 253Fm with a half-life of 3.0 days and 252Fm with a half-life of 25.39 hours.


1. Glenn T. Seaborg, The Transcalifornium Elements., Journal of Chemical Education, Vol 36.1 (1959) p39.
2. Robert E. Krebs, The history and use of our earth’s chemical elements: a reference guide., Greenwood Publishing Group, 2006., p331.
3. Robert J. Silva, The Chemistry of the Actinide and Transactinide Elements., Springer., Vol 3.13, p1628.
3a. Robert J. Silva, The Chemistry of the Actinide and Transactinide Elements., Springer., Vol 3.13, p1626.

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