Fermium

2007 Concise Encyclopedia. Related subjects: Chemical elements

100 einsteinium ← fermium → mendelevium Er ↑ Fm ↓ (Upn) Periodic Table - Extended Periodic Table
General
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
Electronegativity	1.3 (Pauling scale)
Ionization energies	1st: 627 kJ/mol
Miscellaneous
CAS registry number	7440-72-4
Selected 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 - -
References

Fermium ( IPA: /ˈfɛː(r)miəm/) is a synthetic element in the periodic table that has 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.

Notable characteristics

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. There are no known uses of fermium outside of basic research. Fermium is the eighth transuranic element.

History

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 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.

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.

Isotopes

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-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_½ 1.8 seconds). The isotopes of fermium range in atomic weight from 242.073 amu (²⁴²Fm) to 259.101 amu (²⁵⁹Fm).