Fermium (Fm)

Isotopes of Fermium 

Isotope Atomic Mass Half-life Mode of decay Nuclear spin Nuclear magnetic moment
Fm-251 251.08157 5.30 hours EC to Es-251;
α to Cf-247
9/2 No data available 
Fm-252 252.08246 1.058 days α to Cf-248; SF 0 No data available 
Fm-253 253.08517 3 days EC to Es-253;
α to Cf-249
1/2 No data available 
Fm-254 254.08685 3.24 hours α to Cf-250; SF 0 No data available 
Fm-255 255.08995 20.10 hours α to Cf-251; SF 7/2 No data available 
Fm-256 256.09177 2.63 hours α to Cf-252; SF 0 No data available 
Fm-257 257.095099 100.50 days α to Cf-253; SF 9/2 No data available 


Fermium is a radioactive rare earth metal, discovered in 1952 by workers at Argonne and Los Alamos National Laboratories and by Albert Ghiorso and colleagues at the University of California - Berkeley, USA. It was identified in the radioactive debris from a thermonuclear explosion in the Pacific. The longest living isotope is is Fermium-257, with a half-life of 80 days. Fermium takes its name from that of Enrico Fermi, a pioneer in nuclear physics.

Because of the small amounts of produced fermium, as well as the relatively short half-lives of its isotopes, there are no current uses for fermium outside of basic scientific research.

Properties of Fermium

Name Fermium
Symbol Fm
Atomic number 100
Atomic weight [257]
Standard state Presumably a solid at 298 °K
CAS Registry ID 7440-72-4
Group in periodic table N/A 
Group name Actinoid
Period in periodic table 7 (Actinoid)
Block in periodic table f-block
Color Unknown, but probably metallic and silvery white or grey in appearance
Classification Metallic
Melting point About 1800 °K [or 1527 °C or 2781 °F]
Boiling point No data available
Electronegativity 1.3
Electron configuration [Rn]5f127s2

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