Fermium (100)

Fermium [not to be confused with FERRUM] is a synthetic element with symbol Fm and atomic number 100. It is a member of the actinide series. Fermium is a radioactive rare earth metal, whose longest living isotope is ²⁵⁷Fm with a half-life of 80 days. It is of no commercial importance.

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 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

Historical Information  

Fermium is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared. A total of 19 isotopes are known, with ²⁵⁷Fm being the longest-lived with a half-life of 100.5 days.

It was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Enrico Fermi, one of the pioneers of nuclear physics. Its chemistry is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced fermium and all of its isotopes having relatively short half-lives, there are currently no uses for it outside of basic scientific research.

It was then identified in December 1952 by Albert Ghiorso and co-workers at the University of California at Berkeley. They discovered the isotope ²⁵³Es (half-life 20.5 days) that was made by the capture of 15 neutrons by uranium-238 nuclei – which then underwent seven successive beta decays (they added 15 neutrons to the nucleus of a Uranium atom which increased the atomic number, which then released those particles back off (decayed))

Physical properties

• Melting point: about 1800 [or 1527 °C (2781 °F)] K
• Boiling point: no data K

Orbital properties

• Ground state electron configuration:  [Rn].5f¹².7s²
• Shell structure:  2.8.18.32.30.8.2
• Term symbol:   ³H₆
• Pauling electronegativity: 1.3 (Pauling units)
•  First ionization energy: 627 kJ mol^-1
•  Second ionization energy: no data kJ mol^-1