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Technetium (Tc): structure, properties, uses, obtaining

It is a radioactive metal. It has many isotopes, which are technetium atoms with different amounts of neutrons in the nucleus. They occupy the same place on the periodic table but have different atomic masses.

Atomic number symbol and atomic mass of the element technetium. me / CC BY-SA (https://creativecommons.org/licenses/by-sa/2.5). Source: Wikimedia Commons.

All of its isotopes are short-lived compared to Earth, so the technetium generated when the planet was formed has almost all decayed for a long time.

Technetium is produced in nuclear reactors. Its presence has also been detected in stellar matter 

Structure

Its electronic configuration is:

2 2 2 2 6 3 2 3 6 3 10 4 2 4 6 4 5 5 2 ,

or also:

[Kr] 4 5 5 2 .

Below is a Bohr model of the technetium atom where you can see the different orbitals with their electrons around the nucleus.

Electrons in the orbitals of the technetium atom. Ahazard.sciencewriter / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0). Source: Wikimedia Commons.

It crystallizes into a compact hexagonal array or lattice.

Nomenclature

  • Technetium, symbol: Tc
  • 99 Tcm, 99m Tc, Technetium-99m: various ways of indicating the metastable isotope of technetium with atomic mass 99
  • Technetium-95m: metastable isotope with atomic mass 95

Properties

Physical state

Metallic solid with silver glitter.

Technetium coated gold foil. The vial containing it is sealed and filled with the inert gas argon. MARCO CARDIN / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0). Source: Wikimedia Commons.

Standard atomic mass

98

Melting point

2157 ºC

Boiling point

4262 ºC

Density

11 g / cm 3

Solubility

It dissolves in nitric acid (HNO 3 ), in aqua regia (which is a mixture of concentrated HNO 3 and concentrated HCl) and in concentrated sulfuric acid (H 2 SO 4 ). It is insoluble in hydrochloric acid (HCl) or hydrofluoric acid (HF).

Chemical properties

The oxidation states that this element adopts are +4, +5 and +7. Technetium slowly loses its metallic luster when exposed to humid air, as an oxo acid is produced.

It burns in oxygen above 400 ° C to give the oxide Tc 2 O 7  which sublimates (goes from solid to gas directly). Does not react with hydrogen peroxide (H 2 O 2 ).

Isotopes

Technetium has 22 isotopes. Isotopes are atoms of the same element that have different amounts of neutrons in the nucleus, so they have different masses. All are radioactive, therefore unstable, and have atomic masses between 90 and 111.

Specially designed lab hood with glass and lead wall to handle technetium, the isotopes of which are all radioactive. Jejecam / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

Biochemical behavior

Although this element has no biochemical function in living things, it has the ability to chemically bind to many biologically active molecules.

Obtaining

Discovery

It was the first artificially produced item. Its existence had been predicted by the Russian chemist Dmitri Mendeleev in the 19th century, who assigned it its current place on the Periodic Table.

It was not until 1937 that it was discovered in a molybdenum sample that had been bombarded with neutrons in a Berkeley physical laboratory. From that moment began to search in terrestrial materials.

Low natural presence

In 1962 it was found in Africa in a natural mineral uraninite, as a product of the spontaneous fission of uranium-238. Its concentration in this type of rock is extremely small.

Its presence has been detected in some types of stars, which has led to new theories about the production of heavy elements in stellar matter.

Production

It is artificially formed in nuclear reactors from the fission of uranium. It is extracted from spent nuclear fuel rods, in the form of a gray powder.

For every ton of uranium, one milligram of technetium is generated. There are currently very large amounts (tons) that have accumulated over the years.

Obtaining technetium-99m in a laboratory in 1958. Brookhaven National Laboratory. / Public domain. Source: Wikimedia Commons.

Applications

– In the area of ​​nuclear medicine

Technetium-99m (where “m” stands for metastable) is the most widely used isotope. It has a half-life of 6.01 hours. It is widely used for medical diagnostic studies as it emits gamma rays.

Using its combinations with other chemical substances, it is injected into the patients to be evaluated. Once introduced into the body, it is absorbed by certain organs and the gamma rays it emits make it possible to obtain images of various parts of the body.

Injection of compounds with technetium-99m to perform tomography in nuclear medicine. Bionerd / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

Heart

When technetium-99m binds to pyrophosphate, it has the ability to adhere to calcium deposits in the damaged muscles of the heart, allowing evaluation of injuries caused by a heart attack.

Arteries and veins

If combined with a tin compound, it binds to red blood cells and serves to map disorders of the circulatory system .

Spleen

Together with sulfur, it accumulates in the spleen and a clear image of the spleen can be obtained.

Below is an example of the type of images obtained thanks to the gamma rays emitted by technetium-99m:

Scintigraphy images of the neck region where the thyroid is seen. They are obtained with Tc-99m. MBq / Copyrighted free use. Source: Wikimedia Commons.

Bones

Tc-99m is used to evaluate the degree of activity of osteoblasts in a bone lesion. Osteoblasts are the cells in bone that make up the bone matrix.

Scans with this isotope are very sensitive and can detect metastases (spread of cancer cells) and lymphomas in the bones (malignant proliferation of lymphocytes in the bone marrow).

Brain

The 99m Tc ethylcysteinate dimer is readily absorbed by brain tissue, allowing imaging of this organ by single photon emission computed tomography.

– Other uses

In the form of pertechnetate ions (TcO  ) it acts as a corrosion inhibitor for steel, being excellent even in very small amounts. However, it must be used in closed systems due to the radioactivity of technetium.

At the temperature of 11 K (-262.15 ° C) or lower it behaves like an outstanding superconductor.

Technetium-95m is an isotope that has a half-life of 61 days and is used as a radioactive marker or tracer in ecology, for example to track polluting compounds and to study the movement of surface waters.

– Potential applications

It is a more effective catalyst than rhenium (Re) or palladium (Pd) in the dehydrogenation reaction of isopropyl alcohol. Its use in nuclear batteries has also been proposed.

But its radioactivity is a problem for these uses.

Risks

Health

It is radioactive, therefore very harmful to the health of living beings. It is estimated that human exposure to this element is mainly due to the use of 99 Tcm in nuclear medicine.

Symbol indicating radiation hazard. Author: Catalania Catalino. Source: Pixabay.

In such cases, this isotope, after a while, is deposited mainly in the thyroid gland and in the gastrointestinal tract, but according to some studies it is eliminated through the urine within a few days.

Ambient

Because nuclear reactors produce it in large quantities, technetium is an additional cargo that binds to unwanted radioactive waste on the planet.

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