43 Tc (98)

The chemical element technetium is classed as a transition metal. It was discovered in 1937 by Carlo Perrier and Emilio Segrè.

Data Zone Classification: Technetium is a transition metal Color: silver-gray Atomic weight: (98), no stable isotopes State: solid Melting point: 2160 oC, 2433 K Boiling point: 4260 oC, 4533 K Electrons: 43 Protons: 43 Neutrons in most abundant isotope: 55 Electron shells: 2,8,18,14,1 Electron configuration: [Kr] 4d6 5s1 Density @ 20oC: 11.5 g/cm3 Show more, including: Heats, Energies, Oxidation,

Reactions, Compounds, Radii, Conductivities Atomic volume: 8.5 cm3/mol Structure: hcp: hexagonal close packed Specific heat capacity 0.21 J g-1 K-1 Heat of fusion 24.0 kJ mol-1 Heat of atomization 661 kJ mol-1 Heat of vaporization 502 kJ mol-1 1st ionization energy 702.4 kJ mol-1 2nd ionization energy 1472.4 kJ mol-1 3rd ionization energy 2850.2 kJ mol-1 Electron affinity 53 kJ mol-1 Minimum oxidation number -3 Min. common oxidation no. 0 Maximum oxidation number 7 Max. common oxidation no. 7 Electronegativity (Pauling Scale) 1.9 Polarizability volume 11.4 Å3 Reaction with air mild, w/ht, ⇒ Tc 2 O 7 Reaction with 15 M HNO 3 mild, ⇒ HTcO 4 (Pertechnetic acid) Reaction with 6 M HCl none Reaction with 6 M NaOH – Oxide(s) TcO 2 , Tc 2 O 7 Hydride(s) – Chloride(s) TcCl 4 , TcCl 6 Atomic radius 136 pm Ionic radius (1+ ion) – Ionic radius (2+ ion) – Ionic radius (3+ ion) 83 pm Ionic radius (1- ion) – Ionic radius (2- ion) – Ionic radius (3- ion) – Thermal conductivity 50.6 W m-1 K-1 Electrical conductivity 0.001 x 106 S m-1 Freezing/Melting point: 2160 oC, 2433 K

Discovery of Technetium

Dr. Doug Stewart

Technetium’s existence was first predicted by Russian chemist Dmitri Mendeleev, creator of the periodic table. He realized there was a gap in the group 7 transition elements between manganese and ruthenium, and called the element eka-manganese. (2)

In 1925, in Berlin, Germany, Ida Tacke, Walter Noddack, and Otto Berg analyzed a number of platinum ores and columbite minerals. They hoped to find element 43, Mendeleev’s eka-manganese, and also element 75, rhenium. (3)

In the belief that they had achieved their goals, they published X-ray analysis evidence and claimed they had found two new elements. They named element 43 masurium, after the region of Masuria in Prussia where Noddack was born.

Both discoveries were widely disputed when first announced.

Three years later their discovery of element 75, rhenium, was verified while masurium was not. (4)

Today, it has been speculated that Tacke, Noddack and Berg actually did succeed in discovering element 43, now known as technetium. Their samples would have contained uranium, which could have decayed to form technetium-99.

A 1999 study by Dave Curtis and colleagues at Los Alamos National Laboratory, New Mexico reproduced the original researchers’ experiment and obtained very similar results, suggesting that the 1925 discovery could have been correct. (5)

Credit is usually given for the first discovery of technetium to Carlo Perrier and Emilio Segrè in 1937 at the University of Palermo, in Sicily, Italy.

Perrier and Segrè were given a sample of molybdenum by Ernest Lawrence which had been bombarded with deuterium nuclei. They found several technetium isotopes in the sample which were all radioactive. (4)

Technetium was the first element to be produced synthetically.

It is named after the Greek word ‘technètos’ meaning artificial.

Technetium was once thought to exist only in samples produced in the laboratory. However, its spectral lines have now been observed in red giant stars, such as Betelgeuse, shown below.(1)

Tiny amounts also exist in uranium ores.

Technetium’s Periodic Table Neighborhood

Technetium has no stable isotopes – the lightest such element. It is surrounded in the periodic table by elements with stable isotopes.

Appearance and Characteristics

Harmful effects:

Technetium is harmful due to its radioactivity.

Characteristics:

Technetium is a rare, silver-gray metal that tarnishes slowly in moist air.

In powder form, it burns in oxygen to form the heptoxide (Tc 2 O 7 ).

Technetium dissolves in nitric acid and concentrated sulfuric acid, but is not soluble in hydrochloric acid of any strength.

Is an excellent superconductor at temperatures of 11 K and below.

Technetium and promethium are unusual among the light elements, because they have no stable isotopes.

Uses of Technetium

Technetium-99m is a metastable isotope with a half-life of six hours. Technetium-99m emits gamma rays and low energy electrons, forming technetium-99 (half-life 211,000 years). The gamma rays can be photographed using a gamma camera, and technetium-99m is used in 80 to 90 percent of all diagnostic procedures that use radioactive elements.

Technetium-95, with a half-life of 61 days, is used as a radioactive tracer.

Technetium-99, has a very long half-life (2.11 X 105 years) and decays almost entirely by beta decay with no gamma rays. It is used as for equipment calibration.

In small concentrations TcO 4 –, the pertechnetate ion, can protect carbon steels and iron from corrosion. This use is limited to closed systems due to its radioactivity.

Abundance and Isotopes

Abundance earth’s crust: negligible

Abundance solar system: negligible

Cost, pure: per 100g

Cost, bulk: per 100g

Source: Technetium has been found naturally occurring in tiny quantities in uranium ore. The isotope technetium-99 is produced from the waste products of uranium nuclear fuel. Technetium-99m is produced by neutron activation of molybdenum-98 to form molybdenum-99, which has a half-life of 65.94 hours and beta-decays to technetium-99m. The spectral signature of technetium has been detected in light from red giant stars.

Isotopes: Technetium has 26 isotopes whose half-lives are known, with mass numbers from 88 to 113. None are stable. The most stable isotope is 98Tc, with a half-life of 4.2 million years.

References

Image by NASA/ESA Robert E. Krebs, The History And Use of Our Earth’s Chemical Elements: A Reference Guide, 2006, Greenwood Publishing group, p131. Mary Elvira Weeks, The Discovery of the Elements. XX. Recently Discovered Elements, Journal of Chemical Education., March 1933, p164. Per Enghag, Encyclopedia of the Elements: Technical Data – History – Processing – Applications, 2008, John Wiley & Sons, p649-650 John T. Armstrong, Technetium, 2003, American Chemical Society

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