|Name, Symbol, Number||fermium, Fm, 100|
|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|
|Melting point||1800 K
(1527 °C, 2781 °F)
|Oxidation states||2, 3|
|Electronegativity||1.3 (Pauling scale)|
|Ionization energies||1st: 627 kJ/mol|
|CAS registry number||7440-72-4|
Fermium (chemical symbol Fm, atomic number 100) is a synthetic element in the periodic table. A highly radioactive metallic transuranic element 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. 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.
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).
All links retrieved April 6, 2017.
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