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unknown, probably silvery, white or metallic gray
General properties
Name, symbol, number fermium, Fm, 100
Element category actinide
Group, period, block n/a7, f
Standard atomic weight (257)g·mol−1
Electron configuration [Rn] 5f12 7s2
Electrons per shell 2, 8, 18, 32, 30, 8, 2 (Image)
Physical properties
Phase solid
Melting point 1800 K, 1527 °C, 2781 °F
Atomic properties
Oxidation states 2, 3
Electronegativity 1.3 (Pauling scale)
Ionization energies 1st: 627 kJ·mol−1
CAS registry number 7440-72-4
Most stable isotopes
Main article: Isotopes of fermium
iso NA half-life DM DE (MeV) DP
252Fm syn 25.39 h SF - -
α 7.153 248Cf
253Fm syn 3 d ε 0.333 253Es
α 7.197 249Cf
255Fm syn 20.07 h SF - -
α 7.241 251Cf
257Fm syn 100.5 d α 6.864 253Cf
SF - -

Fermium (pronounced /ˈfɜrmiəm/, FER-mee-əm) is a synthetic element with the symbol Fm and atomic number 100. A highly radioactive metallic transuranic element of the actinide series, fermium is made by bombarding plutonium with neutrons and is named after nuclear physicist Enrico Fermi. Fermium is the eighth transuranic element.



Electron shell diagram of fermium

Only small 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 102 (nobelium) was confirmed when 250Fm was chemically identified. Like all synthetic elements it is extremely radioactive and highly toxic. fermium is a metal and not found in nature


There are no known uses of fermium outside of basic research.


Fermium (after Enrico Fermi) was first discovered by a team led by Albert Ghiorso in 1952. The team found 255Fm in the debris of the first hydrogen bomb explosion (see 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 Alamos Scientific Laboratory. All these findings were kept secret until 1955 due to Cold War tensions.[1] Samples of sea coral impacted from the first thermonuclear explosion of November 1952 were used.[2]

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).[3] The Nobel team did not claim discovery until 1954. The isotope they produced was later positively identified as 250Fm.


17 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-lives that are less than 5.4 hours, and the majority of these have half-lives that are less than 3 minutes. This element also has 1 meta state, 250mFm (t½ 1.8 seconds). The isotopes of fermium range in atomic weight from 242.073 u (242Fm) to 259.101 u (259Fm).


  1. ^ Ghiorso, A.; Thompson, S. G.; Higgins, G. H. ; Seaborg, G. T.; Studier, M. H.; Fields, P. R.; Fried, S. M.; Diamond, H.; Mech, J. F.; Pyle, G. L.; Huizenga, J. R.; Hirsch, A.; Manning, W. M.; Browne, C. I.; Smith, H. L.; Spence, R. W. (1955). "New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100". Physical Review 99: 1048–1049. doi:10.1103/PhysRev.99.1048.  
  2. ^ Albert Ghiorso (2003). "Einsteinium and Fermium". Chemical and Engineering News.  
  3. ^ Atterling, Hugo; Forsling, Wilhelm; Holm, Lennart W.; Melander, Lars; Åström, Björn (1954). "Element 100 Produced by Means of Cyclotron-Accelerated Oxygen Ions". Physical Review 95: 585–586. doi:10.1103/PhysRev.95.585.2.  

External links



Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also fermium


Chemical Element: Fm (atomical number 100)


Fermium n

  1. fermium

Simple English

Fermium is a chemical element. It is at position 100 at the periodic table. It is named after Enrico Fermi.


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