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What is fermium?

The fermium (Fm) is a radioactive chemical element obtained from induced manner by nuclear transmutation, in which the reactions of nuclear type are capable of altering artificially core element considered stable, and thus cause an isotope of radioactive nature or an element that does not exist naturally.

This element was discovered in 1952, during the first successful nuclear test “Ivi Mike”, carried out by a group of scientists from the University of California under the direction of Albert Ghiorso. Fermium was discovered as a product of the first hydrogen bomb explosion in the Pacific Ocean.

Years later the fermium was obtained synthetically in a nuclear reactor, bombarding plutonium with neutrons; and in a cyclotron, bombarding uranium-238 with nitrogen ions.

Currently fermium is produced through a long chain of nuclear reactions, which involves bombarding each isotope in the chain with neutrons and then allowing the resulting isotope to undergo beta decay.

Chemical structure of fermium

The atomic number of fermium (Fm) is 100 and its electronic configuration is [Rn] 5 12  7 2 . In addition, it is located within the group of actinides that are part of period 7 of the periodic table and, since its atomic number is greater than 92, it is called a transuranic element.

In this sense, fermium is a synthetic element and therefore has no stable isotopes. For this reason it does not have a standard atomic mass.

Likewise, the atoms – which are isotopes of each other – have the same atomic number, but different atomic mass, considering that there are then 19 known isotopes of the element, ranging from atomic mass 242 to 260.

However, the isotope that can be produced in large quantities on an atomic basis is Fm-257, with a half-life of 100.5 days. This isotope is also the nuclide with the highest atomic number and mass ever isolated from any reactor or material produced by a thermonuclear facility.

Although fermium-257 is produced in larger quantities, fermium-255 has become more available on a regular basis, and is used more frequently for chemical studies at the tracer level.

Fermium properties

The chemical properties of fermium have been studied only with minimal amounts, so that all the available chemical information that has been obtained is from experiments carried out with traces of the element. In fact, in many cases these studies are done with just a few atoms, or even one atom at a time.

According to the Royal Society of Chemistry, fermium has a melting point of 1527 ° C (2781 ° F or 1800 K), its atomic radius is 2.45 Å, its covalent radius is 1.67 Å, ​​and a temperature of 20 ° C is in the solid state (radioactive metal).

Similarly, most of its properties such as oxidation state, electronegativity, density , boiling point , among others, are unknown.

To date, no one has managed to produce a large enough sample of fermium to be seen, although the expectation is that, like other similar elements, it is a silver-gray metal.

Behavior in solutions

Fermium behaves under non-strongly reducing conditions in an aqueous solution as expected for a trivalent actinide ion.

In concentrated hydrochloric acid, nitric acid, and ammonium thiocyanate solutions, fermium forms anionic complexes with these ligands (a molecule or ion that binds to a metal cation to form a complex), which can be adsorbed and then eluted from anion exchange columns.

Under normal conditions, fermium exists in solution as the Fm 3+ ion , which has a hydration index of 16.9 and an acid dissociation constant of 1.6 × 10 -4 (pKa = 3.8); thus the binding in the posterior actinide complexes is believed to be primarily ionic in character.

Likewise, the Fm 3+ ion is expected to be smaller than the preceding An 3+ ions (plutonium, americium or curium ions), due to the greater effective nuclear charge of fermium; therefore, fermium would be expected to form shorter and stronger metal-ligand bonds.

On the other hand, fermium (III) can be quite easily reduced to fermium (II); for example, with samarium (II) chloride, with which fermium (II) co-precipitates.

Electrode normal potential

The electrode potential has been estimated to be approximately -1.15 V relative to the standard hydrogen electrode.

Likewise, the Fm 2+ / Fm 0 pair has an electrode potential of -2.37 (10) V, based on polarographic measurements; that is to say, of voltammetry.

Radioactive decay

Like all artificial elements, fermium undergoes radioactive decay caused mainly by the instability that characterizes it.

This is so due to the combinations of protons and neutrons that do not allow to maintain the balance, and spontaneously change or decay until reaching a more stable form, releasing certain particles.

This radioactive decay occurs through a spontaneous fission through an alpha decomposition (being a heavy element) in californium-253.

Uses and risks

Fermium formation does not occur naturally and has not been found in the earth’s crust, so there is no reason to consider its environmental effects.

Due to the small amounts of fermium produced and its short half-life, there are currently no uses for it outside of basic scientific research .

In this sense, like all synthetic elements, fermium isotopes are extremely radioactive and are considered highly toxic. 

Although few people come into contact with fermium, the International Commission on Radiation Protection has established annual exposure limits for the two most stable isotopes.

For fermium-253, the ingestion limit was set at 107 becquerel (1 Bq is equivalent to one decomposition per second) and the inhalation limit at 105 Bq; for fermium-257, the values ​​are 105 Bq and 4000 Bq, respectively.

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