Fermium is the eighth transuranic element first discovered in 1952 at the debris of the first hydrogen bomb explosion. Owing to small quantity in which it can be produced it has no uses outside basic scientific research.
History and Discovery
Fermium was first discovered and identified by Albert Ghiorso and his co-workers at University of California, Berkeley in 1952. They found element 100 in the debris of the first successful test of a hydrogen bomb, the Ivy Mike nuclear test. The finding of this new element was kept classified on the orders of U.S military because of the on-going cold war tensions. Multiple neutron absorption was considered to be a rare process at that time but analysing the debris resulted in the identification of isotopes of transuranic elements which need absorption of six neutrons by a uranium nucleus for its formation indicating still more neutrons can be captured by uranium nuclei [1]. Berkeley team also managed to prepare element 100 in laboratory. Meanwhile another group at Stockholm, Nobel Institute for Physics, independently produced an isotope of fermium by bombarding oxygen-16 ions in a uranium target. Both groups published their work in 1954 [2]. The Ivy Mike studies of the element were published in 1955. Priority was given to Berkeley team and they were given the chance to name the element. The element was suggested to be named after the scientist Enrico Fermi, one of the pioneers of nuclear physics and who was the developer of the artificial self-sustained nuclear reactor.
Fermium
| Periodic Table Classification | Group n/a Period 7 |
|---|---|
| State at 20C | Solid (predicted) |
| Color | n/a |
| Electron Configuration | [Rn] 5f12 7s2 |
| Electron Number | 100 |
| Proton Number | 100 |
| Electron Shell | 2, 8, 18, 32, 30, 8, 2 |
| Density | 9.70 g.cm-3 at 20°C (predicted) |
| Atomic number | 100 |
| Atomic Mass | 257.00 g.mol -1 (most stable isotope) |
| Electronegativity according to Pauling | 1.30 |
Occurrence
Fermium did occur naturally, like other transuranic element, at the natural nuclear fission reactor at Oklo but is no longer the case. Natural transformation of actinides in earth’s crust to fermium is extremely unlikely event as it requires multiple neutron capture. Hence, all the existing fermium on earth is man-made and is produced in nuclear weapon tests, high power nuclear reactors or in laboratories where it exists for few days because of its short half-life. It is produced in minute quantity by bombardment of neutrons on lighter actinides in high flux nuclear reactors. It is the last element that can be prepared in macroscopic quantity as it is heaviest element that can be produced by neutron bombardment of lighter elements [3]. No known isotope of fermium undergo beta minus decay to the next element, making fermium the last element that can be produced by neutron capture process. Because of its highly unstable nature any fermium formed at the time of formation of earth would have decayed by now.
Physical Characteristics
Fermium has not yet been prepared in pure form so not much is known about its physical characteristics. It is expected to be a solid with a predicted melting point of 1527 degree centigrade and density of 9.7 g/cm3. Fermium belongs to the actinide series and has an atomic number 100 while it is represented by symbol Fm.
Chemical Characteristics
No solid compounds of the element fermium have been prepared and its chemistry has only been studied using tracer techniques in solution form. It has the most stable oxidation state of +3 but divalent state can also be achieved unlike many other actinides. Fermium, under normal conditions, exist as Fm +3 ions in solution forming complexes which are more stable than complexes of preceding actinides.
Significance and Uses
- Fermium has currently no known uses apart from its use in basic scientific research.
Health Effects
Not much data of toxicity of fermium is available because of it being a rare element. It does not occur naturally and also has relatively short half-life.
Isotopes of Fermium
Fermium has twenty known isotopes. The atomic weight of these nuclides ranges from 241 to 260. The most stable isotope of fermium is fermium-257 that has a half-life of 100.5 days. The next stable isotope is fermium-253 with a half-life of three days. All the remaining isotopes have half-life ranging from few hours to less than a millisecond [4]. Heavier nuclides are unstable and undergo spontaneous fission making nuclides with mass number greater than 257 impossible to be created by neutron capture and can only be made in a nuclear explosion.
REFERENCES
[1]. Ghiorso, A.; Thompson, S.; Higgins, G.; Seaborg, Glenn T.; Studier, M.; Fields, P.; Fried, S.; Diamond, H.; et al. (1955). “New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100”. Phys. Rev. 99(3): 1048–1049.
[2]. Atterling, Hugo; Forsling, Wilhelm; Holm, Lennart W.; Melander, Lars; Åström, Björn (1954). “Element 100 Produced by Means of Cyclotron-Accelerated Oxygen Ions”. Physical Review. 95 (2): 585–586.
[3]. Ghiorso, Albert (2003). “Einsteinium and Fermium”. Chemical and Engineering News. 81 (36): 174–175.
[4]. Silva, Robert J. (2006). “Fermium, Mendelevium, Nobelium, and Lawrencium” (PDF). In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements. 3(3rd ed.). Dordrecht: Springer. pp. 1621–1651