Fermium

einsteinium ← fermium → mendelevium Er ↑ Fm ↓ (Upn) 100Fm Periodic table
Appearance
unknown, probably silvery, white or metallic gray
General properties
Name, symbol, number	fermium, Fm, 100
Pronunciation	/ˈfɜrmiəm/ FER-mee-əm
Element category	actinide
Group, period, block	n/a, 7, 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
Miscellanea
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.

Characteristics

Electron shell diagram of fermium

Only small amounts of fermium have been produced or isolated. Thus, relatively little is known about its chemical properties. Only the +3 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.

History

Fermium, named for the Italian-American physicist Enrico Fermi, was first discovered by a team led by Albert Ghiorso in 1952. The team found ²⁵⁵Fm in the collected dust from the first hydrogen bomb explosion on November 1, 1952. See the Ivy Mike H-bomb test. This isotope was created when U-238 combined with 17 neutrons during the intense temperatures of the nuclear test explosion. Eight beta decays also occurred to create fermium nuclei. This work was overseen by the University of California Radiation Laboratory, the Argonne National Laboratory, and the 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 also used.^[2]

In late 1953 and early 1954 a team from the Nobel Institute for Physics in Stockholm, Sweden, bombarded a uranium-238 target with oxygen-16 ions, producing an alpha-emitting element with an atomic mass of about 250 and with 100 protons (in other words, element ²⁵⁰Unn).^[3] The Nobel Insitute's team did not claim this discovery until 1954. The isotope that 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 about 100 days, ²⁵³Fm with a half-life of three days, ²⁵²Fm with a half-life of 25.4 hours, and ²⁵⁵Fm with a half-life of 20.1 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 three minutes. Fermium also has one known metastable state, ^250mFm (t_½ 1.8 seconds). The isotopes of fermium range in atomic mass from 242.073 atomic mass units (²⁴²Fm) to 259.101 a.m.u. (²⁵⁹Fm).

References

• Los Alamos National Laboratory - Fermium
• Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
• It's Elemental - Fermium

External links

• WebElements.com - Fermium