Name: Fermium
Symbol: Fm
Atomic Number: 100
Atomic Weight: 257.000000
Family: Rare Earth Elements
CAS RN: 7440-72-4
Description: A radioactive rare earth metal.
State (25C): Solid
Oxidation states: +3

Molar Volume: unknown
Valence Electrons: 5f127s2

Boiling Point: unknown
Melting Point: 1800oK, 1527oC, 2781o

Elec. Energy Level.: 2, 8, 18, 32, 30, 8, 2
Isotopes: 19 + None Stable
Heat of Vaporization: unknown
Heat of Fusion: unknown
Density: unknown
Specific Heat: unknown       
Atomic Radius: unknown
Ionic Radius: unknown 
Electronegativity: 1.3 (Pauling), 1.2 (Allrod Rochow)

1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10f12 6s2p6 7s2


Fermium (after Enrico Fermi) was first discovered by a team led by Albert Ghiorso in 1952.  The team found 255Fm (half-life ~20 hrs.)  in the debris of the first hydrogen bomb explosion (Operation Ivy).  That isotope was created when 238U combined with 17 neutrons in the intense temperature and pressure of the explosion (eight beta decays also occurred to create the element). The work was overseen by the University of California Radiation Laboratory, Argonne National Laboratory, and Los Alomos Scientific Laboratory whose team members included Ghiorso, Stanley G. Thompson, Gary H. Higgins, Glenn T. Seaborg (from the Radiation Laboratory and Department of Chemistry of the University of California), Martin H. Studier, P.R. Fields, Sherman M. Fried, H. Diamond, J.F. Mech, G.L. Pyle, John R. Huizenga, A. Hirsch, W.M. Manning (from the Argonne National Laboratory), C.I. Browne, H. Louise Smith, and R.W. Spence (from the Los Alamos Scientific Laboratory). Samples of sea coral impacted from the first thermonuclear explosion of November 1952 were used.

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Enrico Fermi

All these findings were kept secret until 1955 due to Cold War tensions.  In late 1953 and early 1954 a team from the Nobel Institute of Physics in Stockholm bombarded a 238U target with 16O ions, producing an alpha-emitter with an atomic weight of ~250 and with 100 protons (in other words, element 250100).  The Nobel team did not claim discovery but the isotope they produced was later positively identified as 250Fm.


Only tracer amounts of fermium have ever been produced or isolated. Thus relatively little is known about its chemical properties. Only the (III) oxidation state of the element appears to exist in aqueous solution. 254Fm and heavier isotopes can be synthesized by intense neutron bombardment of lighter elements (especially uranium and plutonium).  During this, successive neutron captures mixed with beta decays build the fermium isotope. The intense neutron bombardment conditions needed to create fermium exist in thermonuclear explosions and can be replicated in the laboratory (such as in the High Flux Isotope Reactor at Oak Ridge National Laboratory).  The synthesis of element nobelium-102 was confirmed when 250Fm was chemically identified.   There are no known uses of fermium outside of basic research.  Fermium is the eighth transuranic element.

2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10 5f12
6s2 6p6


Fermium does not exist naturally on Earth today but it has occurred in the past, produced in natural reactor deposits.  Annual world production of fermium probably totals less than a milllonth of a gram.

Today, fermium is produced though a lengthy chain of nuclear reactions that involves bombarding each isotope in the chain with neutrons and then allowing the resulting isotope to undergo beta decay.  Fermium doesn't occur naturally, and has not been found in the earth's crust, so there is no reason to consider its health hazards.  Due to the small amounts produced and its short half-life, there are currently no uses for fermium outside of basic scientific research.


19 radioisotopes of fermium have been characterized, with the most stable being 257Fm with a half-life of 100.5 days, 253Fm with a half-life of 3 days, 252Fm with a half-life of 25.39 hours, and 255Fm with a half-life of 20.07 hours.  All of the remaining radioactive isotopes have half-lifes that are less than 5.4 hours, and the majority of these have half lifes that are less than 3 minutes. This element also has 1 meta state, 250mFm (t 1.8 seconds). The isotopes of fermium range in atomic weight from 242.073 amu (242Fm) to 259.101 amu (259Fm).

Fermium's most stable isotope, fermium-257, decays into californium-253 through alpha decay or decays through spontaneous fission.

250Fm, with a half-life of 30 minutes, has been shown to be a decay product of element 254No. Chemical identification of 250Fm confirmed the production of element 102.

254Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements, such as plutonium, using a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached.

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Isotope Atomic Mass Half-Life Isotope Atomic Mass Half-Life
242Fm 242.073 0.8 ms 251Fm 251.0816 5.3 hours
243Fm 243.075 0.18 seconds 252Fm 252.0825 25.39 hours
244Fm 244.074 3.3 ms 253Fm 253.0852 3 days
245Fm 245.075 4.2 seconds 254Fm 254.0869 3.24 hours
246Fm 246.0735 1.1 seconds 255Fm 255.09 20.07 hours
247Fm 247.077 35 seconds 256Fm 256.0918 157.6 minutes
247mlFm   9.2 seconds 257Fm 257.0951 100.5 days
248Fm 248.0772 3.6 seconds 258Fm 258.097 370 us
249Fm 249.079 2.6 minutes 259Fm 259.101 1.5 seconds
250Fm 250.0795 30 minutes 260Fm   ~4ms

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Fermium Data


Atomic Structure

Atomic Radius (): unknown
Atomic Volume: unknown
Covalent Radius: unknown
Crystal Structure: unknown
Ionic Radius: unknown

Chemical Properties

Electrochemical Equivalent: 3.1974 g/amp-hr
Electron Work Function: unknown
Electronegativity: 1.3 (Pauling), 1.2 (Allrod Rochow)
Heat of Fusion: unknown
First Ionization Potential: 6.5
Second Ionization Potential: unknown
Third Ionization Potential: unknown
Valence Electron Potential (-eV): unknown
Ionization Energy (eV): 6.50 eV

Physical Properties

Atomic Mass Average: 257
Boiling Point: unknown
Melting Point: 1800oK, 1527oC, 2781oF
Heat of Vaporization: unknown
Coefficient of Lineal Thermal Expansion/K-1: N/A
Electrical Conductivity: unknown
Thermal Conductivity: 0.1 W/cmK
Density: unknown
Enthalpy of Atomization: unknown
Enthalpy of Fusion: unknown
Enthalpy of Vaporization: unknown
Molar Volume: unknown
Specific Heat: unknown
Vapor Pressure: unknown
Estimated Crustal Abundance: unknown
Estimated Oceanic Abundance: unknown