Technetium Facts – Atomic Number 43 Element Symbol Tc

Technetium is a transition metal element with atomic number 43 and element symbol Tc. It is the lightest radioactive element. Traces of technetium occur naturally, but it was discovered through synthesis in a lab and was the first artificial element. You won’t encounter technetium in daily life, but the isotope technetium-99 is used in nuclear medicine. Here is a collection of technetium facts, including its discovery, sources, and uses.

Technetium Element Facts

Name: Technetium

Atomic Number: 43

Element Symbol: Tc

Atomic Weight: [97]

Appearance: Shiny gray metal

Group: Group 7

Period: Period 5

Block: d-block

Element Family: Transition metal

Electron Configuration: [Kr] 4d⁵ 5s²

Electrons per Shell: 2, 8, 18, 13, 2

Discovery: Emilio Segrè and Carlo Perrier (1937)

Name Origin: Greek technikos: an art or technetos: artificial

History of Discovery

From 1828 to 1908, many scientists claimed discovery of element 4. They suggested element names, including polinium, ilmenium, pelopium, davyum, lucium, and nipponium. In 1925, German chemists Walter Noddack, Otto Berg, and Ida Tacke reported discovery of element 43, which they named masurium. The researchers obtained an x-ray signal corresponding to element 43 from a sample of columbite bombarded with neutrons. The discovery could not be replicated, so the group did not get credit. However, element 43 was sometimes called masurium in publications after this date. Whether or not Noddack, Berg, and Tacke discovered the element remains a subject of debate.

Official credit for the discovery goes to Carlo Perrier and Emilio Segrè, at the University of Palermo in Sicily. In 1937, the researchers isolated technetium-95m and technetium-97 from radioactive molybdenum foil from a cyclotron. The University of Palermo wanted to name the element “panorium” after the Latin name for Palermo, Panormus. But, Perrier and Segrè chose the name technetium, from the Greek work for “artificial” because it was the first element to be made artificially.

Technetium Isotopes

There are over 30 technetium isotopes, with mass numbers ranging from 85 to 118. The most stable isotopes are technetium-97 (half-life of 4.21 million years), technetium-98 (half-life of 4.2 million years), and technetium-99 (half-life of 211,100 years). Most isotopes have a half-life under one hour. Beta emission and electron capture are the most common decay modes.

There are many technetium nuclear isotopes, which are isotopes that have one or more excited nucleons. The most stable is technetium-97m, with a half-life of 91 days. Technetium-99m has a half-life of 6.01 hour and emits gamma radiation.

Biological Role and Toxicity

Technetium serves no biological role in any organism. Usually, it isn’t found in the human body. While the element has low toxicity, it poses a hazard because of its radioactivity. The nature of the risk depends on the isotope. Technetium-99 (the most common isotope) is a weak beta emitter, so its radiation is stopped by glassware. For this isotope, inhalation poses the greatest risk, as the radiation can cause lung cancer. Usually, it’s safe to handle technetium simply using a fume hood.

Technetium Sources

Technetium is a very rare element in the Earth’s crust, with an abundance of about 0.003 parts per trillion. None of the primordial technetium present when the Earth was formed has survived to the present day because of its half-life. The small amount that exists comes from spontaneous fission of uranium in its ores. Some red giants, known as technetium stars, show an absorption line indicating they contain the element.

So, technetium is produced artificially. Most technetium-99 comes from spent nuclear fuel rods of nuclear reactors. The isotope comes from nuclear fission of uranium-235 and plutonium-239. However, only a fraction of the element produced in this manner is recovered and used. Most of it becomes radioactive waste. Technetium also occurs in nuclear fallout from fission bombs. Other sources of technetium include neutron activation of molybdenum-99 and bombardment of molybdenum targets in particle accelerators.

Prior to the nuclear age, the element wasn’t found in living organisms. Now, minute quantities occur in fish and other aquatic life.

Technetium Uses

The primary use of technetium is for nuclear medicine. Technetium-99m (where “m” indicates a metastable isomer) is a radioactive tracer for diagnostic tests and imaging. The isotope technetium 95m has a longer half-life and is used as a radioactive tracer for environmental movement of the element in plants and animals.

Technetium-99 is a National Institute of Standards and Technology (NIST) beta emitter standard. This isotope may find use in nanoscale nuclear batteries and optoelectronic device.

Technetium acts as a catalyst, similar to rhenium and palladium, but its use is limited by its radioactivity. Small amounts of technetium added to steel protect it from corrosion, even at high temperatures. Here again, radioactivity limits its usefulness.

Technetium Compounds

Technetium forms many compounds and complexes. One of the most commonly produced compounds is sodium pertechnetate (Na[TcO₄]), which is produced from [⁹⁹MoO₄]²⁻ radioactive decay. Technetium heptoxide (Tc₂O₇) is a rare example of a molecular metal oxide (other examples including OsO₄ and RuO₄). The element forms dioxide, disulfide, diselenide, and ditelluride. Technetium forms organometallic complexes with Tc-C bonds. It forms coordination complexes with organic ligands, which are often used in nuclear medicine.

Physical Data

Density (room temperature): 11 g/cm³

Melting Point: 2430 K ​(2157 °C, ​3915 °F)

Boiling Point: 4538 K ​(4265 °C, ​7709 °F)

State at 20ºC: Solid

Heat of Fusion: 33.29 kJ/mol

Heat of Vaporization: 585.2 kJ/mol

Molar Heat Capacity: 24.27 J/(mol·K)

Thermal Expansion: 7.1 µm/(m·K) (at r.t.)

Thermal Conductivity: 50.6 W/(m·K)

Electrical Resistivity: 200 nΩ·m (at 20 °C)

Crystal Structure: hexagonal close-packed (hcp)

Magnetic Ordering: Paramagnetic

Atomic Data

Atomic Radius: empirical: 136 pm

Covalent Radius: 147±7 pm

Electronegativity: Pauling scale: 1.9

1st Ionization Energy: 702 kJ/mol

2nd Ionization Energy: 1470 kJ/mol

3rd Ionization Energy: 2850 kJ/mol

Oxidation States: −3, −1, 0, +1, +2, +3, +4, +5, +6, +7

Interesting Technetium Facts

• Part of the reason technetium is radioactive while other elements near it on the periodic table are stable is because the technetium atom has an odd number of protons. The odd number means a proton remains unpaired, giving the nucleus a net spin.
• Technetium is a type-II superconductor below a temperature of 7.46 K.
• The discovery of technetium in red giants in 1952 helped to prove that stars produce heavy elements.
• Technetium tarnishes in moist air.
• Powdered technetium burns in oxygen.
• The physical properties of technetium are intermediate between those of rhenium and manganese.
• Technetium has many oxidation states, but the +4, +5, and +7 oxidation states are the most common.
• Although it is a transition metal, technetium doesn’t usually form cations. It tends to form covalent bonds.
• Technetium dissolves in aqua regia, nitric acid, and sulfuric acid, but does not dissolve in hydrochloric acid.

References

• Emsley, John (2001). “Uranium”. Nature’s Building Blocks: An A to Z Guide to the Elements. Oxford: Oxford University Press. pp. 476–482. ISBN 978-0-19-850340-8.
• Jonge; Pauwels, E. K. (1996). “Technetium, the missing element”. European Journal of Nuclear Medicine. 23 (3): 336–44. doi:10.1007/BF00837634
• Weast, Robert (1984). CRC Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 0-8493-0464-4.
• Zingales, R. (2005). “From Masurium to Trinacrium: The Troubled Story of Element 43”. Journal of Chemical Education. 82 (2): 221–227. doi:10.1021/ed082p221