From New World Encyclopedia
100 einsteiniumfermiummendelevium


periodic table
Name, Symbol, Number fermium, Fm, 100
Chemical series actinides
Group, Period, Block n/a, 7, f
Appearance unknown, probably silvery
white or metallic gray
Atomic mass (257) g/mol
Electron configuration [Rn] 5f12 7s2
Electrons per shell 2, 8, 18, 32, 30, 8, 2
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
CAS registry number 7440-72-4
Notable 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 (chemical symbol Fm, atomic number 100) is a synthetic element in the periodic table. A highly radioactive metallic transuranic element[1] of the actinide series, it is made by bombarding plutonium with neutrons. Fermium is of interest mainly for basic research, and no applications have yet been developed.


Fermium was named after nuclear physicist Enrico Fermi. It 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.[2] Samples of sea coral impacted from the first thermonuclear explosion of November 1952 were used.

All these findings were kept secret until 1955 due to Cold War tensions, however. 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.

Notable characteristics

Fermium is an inner transition metal of the actinide series, located in period 7 of the periodic table, between einsteinium and mendelevium. It is the eighth transuranic element.

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.


Many 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 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 three minutes. This element also has one meta state, 250mFm (t½ 1.8 seconds). The isotopes of fermium range in atomic weight from 242.073 amu (242Fm) to 259.101 amu (259Fm).

See also


  1. "Transuranic elements" are the chemical elements with atomic numbers greater than that of uranium (atomic number 92).
  2. Members of the research team included Albert 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).

ISBN links support NWE through referral fees

  • Emsley, John. Nature's Building Blocks: An A–Z Guide to the Elements. Oxford: Oxford Univ. Press, 2001. ISBN 0198503407
  • Greenwood, N. N., and A. Earnshaw. Chemistry of the Elements 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann, 1998. ISBN 0750633654. Online version. Retrieved July 21, 2022
  • Hampel, Clifford A. The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corp, 1968. ISBN 0442155980
  • Morss, Lester R., Norman M. Edelstein and Jean Fuger (eds.). The Chemistry of the Actinide and Transactinide Elements. 3rd ed. 5 vols. Joseph J. Katz, adapter. Dordrecht: Springer, 2006. ISBN 1402035551
  • Stwertka, Albert. Guide to the Elements. Rev. ed. Oxford: Oxford University Press, 1998. ISBN 0195080831

External links

All links retrieved April 6, 2017.


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