Technetium (Tc)

• Element Symbol: Tc
• Atomic Number: 43
• Atomic Mass: 98
• Group # in Periodic Table: 7
• Group Name: Transition metals
• Period in Periodic Table: 5
• Block of Periodic Table: d-block
• Discovered by: Carlo Perrier, Emilio Segrè (1937)

Technetium is an artificial, synthetic chemical element of the periodic table. It is considered a transition metal, a classification that includes nine different groups and elements such as titanium, zinc, and gold. Transition metals typically form colored compounds and have strong valence, or the ability of an atom to connect chemically to another atom. Technetium was the first artificial element to be created.

When Russian chemist Dmitri Mendeleev first developed the periodic table in the mid-1800s, it contained many gaps between elements. One such gap in group 7, between the elements manganese and ruthenium, prompted Mendeleev to predict that a then-unknown element would be discovered to fill the hole. He tentatively dubbed the undiscovered element "eka-manganese" (eka being Sanskrit for "one," meaning the element would be one space below manganese) but was unable to prove its existence during his lifetime.

Many scientists tried to prove Mendeleev’s theory in subsequent years, mostly without success. In 1925 in Berlin, scientists Walter Noddack, Ida Noddack (née Tacke), and Otto Berg attempted to prove the mysterious element’s existence. Through analysis of various minerals and platinum ores, the team discovered what they believed to be element 43, which they named "masurium," as well as another element, rhenium. This discovery was the subject of much debate at the time, and although their finding of rhenium was confirmed, it is still unclear whether or not the team actually found element 43.

The discovery of technetium is instead attributed to scientists Carlo Perrier and Emilio Segrè. While working at the University of Palermo in Italy in 1937, Perrier and Segrè began experimenting with a sample of the element molybdenum that they had obtained from the Lawrence Radiation Laboratory in Berkeley, where it had been exposed to radiation. Perrier and Segrè bombarded the sample with deuterons, or the nuclei of deuterium atoms, and successfully isolated a sample of the elusive element 43. They named the element "technetium" after the Greek word for "artificial," because it was the first artificial element to be discovered.

Physical Properties

Technetium is a silvery-gray metal, and it is usually obtained in a gray powered form. At 298 kelvins (K), technetium’s standard state is solid, with a density of 11.5 grams per cubic centimeter (g/cm³). Technetium metal is susceptible to corrosion when exposed to moist air, but in powdered form it burns in oxygen. The melting point of technetium is 2157 degrees Celsius (°C), and its boiling point is 4625 °C. These values are quite high, which is a common characteristic of transition metals. The specific heat of technetium at 298 K is 63 joules per kilogram-kelvin (J/kg·K). Technetium is considered an excellent conductor and is classified as a superconductor at temperatures of −262 °C or below, with an electrical conductivity of 5 × 10⁶ siemens per meter (S/m). Its thermal conductivity is 51 watts per meter-kelvin (W/m·K). Technetium is paramagnetic, which means that it is magnetized when placed within a magnetic field but does not retain this property upon removal.

Chemical Properties

The most common oxidation states of technetium are +7, +5, and +4. Technetium has a hexagonal, close-packed crystal structure, and it can be chemically bound to many active molecules, dissolving readily in nitric acid and aqua regia. All isotopes of technetium are radioactive, making it the lightest element to have no stable isotopes. Of the more than thirty radioactive technetium isotopes that exist, the most stable is technetium-98, with a half-life of 4.2 million years. With a few exceptions, all of the remaining technetium isotopes have half-lives that are less than one hour.

Unstable technetium isotopes with mass numbers less than 98 (technetium’s most stable isotope) undergo electron capture, a form of radioactive decay in which an atom’s electron is absorbed by the nucleus and combines with a proton to form a neutron and a neutrino. In technetium, this process usually results in molybdenum isotopes. Unstable technetium isotopes with mass numbers greater than 98 undergo beta decay, another form of radioactive decay, in which a proton is converted into a neutron (or vice versa) inside the nucleus of an atom, causing the atom to release energy in the form of a beta particle (a fast-moving electron or positron). In technetium, this usually produces isotopes of ruthenium.

Applications

Technetium is primarily obtained artificially, and any amounts that do exist naturally are very small. In 1962 technetium was found in the mineral pitchblende, a common uranium ore found in Africa, as a result of spontaneous fission of a uranium isotope. However, this was a rare appearance of the element, and most of the technetium that is produced comes from nuclear fuel rods located in nuclear research facilities. These fuel rods produce large amounts of technetium in comparison to other fission by-products, making technetium a significant source of unwanted radioactive waste.

Despite only existing in Earth’s crust in miniscule amounts, technetium was identified in the emission spectra of certain red giant stars in the 1950s. This discovery has supported the theory of certain scientists that heavy elements can be synthesized inside stars. Technetium is regarded as highly toxic due to the radioactive nature of all of the element’s isotopes. If inhaled as a powder, it can create a high risk for lung cancer.

Also due to its highly radioactive nature, technetium has only a few specific practical applications. The most utilized form of technetium is its metastable isotope, technetium-99m, which has a half-life of six hours. This isotope emits gamma rays and is used in diagnostic practices in the medical field. When photographed using a highly specialized camera, these gamma rays provide imaging of areas such as the heart, liver, and brain. Additionally, when small amounts of technetium are added to steel, the combination provides extreme anticorrosion protection, even at temperatures as high as 206.85 °C. However, due to the toxic nature of the element, this combination can only be employed in specific, isolated cases to avoid contamination or exposure.

Bibliography

Crabtree, Robert H. The Organometallic Chemistry of the Transition Metals. 6th ed. Hoboken: Wiley, 2014. Print.

Emsley, John. Nature’s Building Blocks: An A–Z Guide to the Elements. 2nd ed. New York: Oxford UP, 2011. Print.

Halka, Monica, and Brian Nordstrom. Transition Metals. New York: Facts on File, 2011. Print.

Haynes, William M, ed. CRC Handbook of Chemistry and Physics. 95th ed. Boca Raton: CRC, 2014. Print.

"Technical Data for Technetium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 13 Aug. 2015.