Technetium

Technetium (Tc)

Introduction

Technetium is a chemical element with atomic number 43 in the periodic table. It’s a synthetically produced element, but it can also be found in Earth’s crust. The natural occurrence of element 43 is around 0.003 parts per trillion. 

 

As a member of the manganese family of elements, technetium is a divalent transition metal. It’s mainly used as a radioactive tracer in nuclear medicine, especially its technetium-99 isotope. 

Fact Box

Chemical and Physical Properties of Technetium

The symbol in the periodic table of elements: Tc

Atomic number: 43

Atomic weight (mass): 

Group number: 7 (Transition metals)

Period: 5 (d-block)

Color: Silver

Physical state: Solid at room temperature

Half-life: From 110 nanoseconds to 4.21 million years

Electronegativity according to Pauling: 1.9

Density: 11.5 g.cm-3 at 20°C

Melting point: 2157°C, 3915°F, 2430 K

Boiling point: 4262°C, 7704°F, 4535 K

Van der Waals radius: 0.128 nm

Ionic radius: 1.95 Å

Isotopes: 33

Most characteristic isotope: 97Tc, 99Tc

Electronic shell: [Kr] 4d55s2

The energy of the first ionization: 7.28 eV

The energy of the second ionization: N/A

Discovery date: In 1937 by Carlo Perrier and Emilio Segrè

 

Located between the elements manganese and rhenium on the periodic table, technetium has the symbol Tc, atomic number 43, atomic mass of (99) g.mol-1, and electron configuration [Kr] 4d55s2. Element 43 is a silver metal with a hexagonal crystal structure. Its boiling point is 4262°C, 7704°F, 4535 K, while the melting point is achieved at 2157°C, 3915°F, 2430 K. This member of the manganese group of elements in the periodic table has an electronegativity of 1.9 according to Pauling, whereas the atomic radius according to van der Waals is 0.128 nm. 

 

Being classified as a transition metal, technetium is an excellent superconductor and a remarkable corrosion inhibitor. It also has strong paramagnetic properties. However, oxygen exposure to the technetium metal may trigger a very slow process of tarnishing. Namely, it slowly tarnishes in moist air, while its powder form burns when exposed to O2. In addition, element 43 readily reacts with sulfuric acid, nitric acid, as well as with aqua regia. Technetium is not soluble in any concentration of hydrochloric acid.                 

How Was Technetium Discovered?

When the Japanese chemist Masataka Ogawa claimed to have discovered one of Mendeleev’s predicted elements in 1908, no other scientist was able to confirm his scientific data. In this way,  ‘eka-manganese’ (technetium) was still left to be a puzzle to solve for the scientists of the world.

The Contribution of Walter Noddack, Ida Tacke, and Otto Berg

In 1923, a team of German chemists that included the chemists Walter Noddack (1893-1960), Ida Tacke-Noddack (1896-1979), and Otto Berg attempted to discover the two missing elements of Mendeleev’s periodic system of elements in a sample of molybdenum. 

 

Employed at the Physikalisch-Technische Reichsanstalt (PTR) laboratory located in Berlin-Charlottenburg, Western Germany, these three scientists concluded that the elements with an odd-atomic number were less abundant than those with an even-atomic number. This led Noddack, Tacke, and Berg to the idea that they should look for the elusive eka-manganese element in platinum and columbite ores because many rare elements have already been traced in these particular ores. Before embarking on the projected goal, Tacke took a whole year to first study the chemical separation procedures required for their research mission. 

 

After thorough preparation and following Mosley’s new concept for classification of elements, the German team of scientists identified the elements 43 (masurium, today named as technetium), and 75 (rhenium). Unfortunately, Noddack, Tacke, and Berg were unable to reproduce the methods that led them to the discovery of element 43. The reason behind their failure to confirm the previously obtained scientific evidence was that element 43 had no stable isotopes. They also needed a particle accelerator for their confirmation research which hadn’t been invented until 1929. 

The Discovery of Emilio Segrè 

In 1937, the Italian-American physicist and Nobel laureate Emilio Segrè (1905-1989) together with the Italian mineralogist Carlo Perrier (1886-1948) led a group of Italian scientists at the University of Palermo, Sicily, Italy, throughout the investigation of a deflector foil segment from a molybdenum-made cyclotron. This particle accelerator was previously used to smash atoms of molybdenum by deuterons at the Berkeley Laboratories in California, United States. 

 

Segrè and Perrier exposed the sample to high-energy radiation, the two scientists discovered a different color line on the spectrum, which pointed out the presence of a new chemical element. After they managed to isolate one ten-billionth of a gram, they analyzed the properties of the new element and concluded that it belongs to the gap of element 43, as predicted by Mendeleev. 

How Did Technetium Get Its Name?

The name is derived from the Greek word ‘technetos‘ meaning artificial because technetium is the first element that has been artificially produced. However, minuscule amounts of element 43 can still be traced in nature.

Where Can You Find Technetium?

In 1952, the American astronomer and specialist in spectroscopy Paul W. Merrill (1887-1961) detected the presence of element 43 in the S-type, M-type, and N-type stars of our Universe by analyzing the light they produce. Its natural occurrence is almost non-existent. For this reason, technetium today is mainly produced from the spent nuclear fuel rods in large quantities. 

 

However, in 1962, two chemists employed at the Department of Chemistry, University of Arkansas, Fayetteville, United States, succeeded in what then seemed impossible – isolating the elusive element from a terrestrial material. By observing an African pitchblende sample (a uranium-rich ore) as a spontaneous fission product of uranium-238, B.T. Kenna and P.K. Kuroda detected the first naturally occurring isotope of technetium 99Tc. 

 

Technetium in Everyday Life

Until the present, only minuscule amounts of this radioactive chemical element have some form of application, which can be observed in the instances given below:

 

  • The Tc-99m is a gamma-rays emitting isomer of element 73 that is used in medical diagnostic studies because it’s able to make chemical bonds with many biologically active molecules. Used as a radioactive tracer, it can also be injected in some body parts. In this way, the radiation that is immediately emitted indicated the potential problem with the particular organ or tissue;
  • When a small percent of technetium is added to steel, this chemical element offers strong corrosion protection to the iron alloy. Mild carbon steels can be protected by only 55 ppm of KTcO4 added to the alloy.
  • As a catalyst, technetium is more suitable than rhenium or palladium when it comes to the dehydrogenation of isopropyl alcohol;
  • Optoelectric nuclear batteries are also made with a small quantity of element 43.

How Dangerous Is Technetium?

As a highly radioactive metal, technetium is both a toxic and dangerous substance. It requires the highest protection measures of the person who is working with this substance. Being a powerful contamination hazard, this chemical should be handled in a glove box. 

 

However, due to its extremely small presence in nature, the radioactive isotopes of element 43 are used in radiology as a radioactive tracer of blockages outside the body. Tc-99, a decay product of Molybdenum-99, is the most used diagnostically as a radioactive imaging agent. 

Environmental Effects of Technetium

The trace-quantities of technetium that may occur in nature today are largely produced by spontaneous fission or neutron capture by molybdenum. Namely, nuclear reactors produce tons of technetium nowadays, which results in even larger quantities of unwanted radioactive waste that heavily pollutes the environmental systems and poses a great risk upon all living forms. 

Isotopes of Technetium

Element 43 has 33 radioactive isotopes with a short half-life. As with all radioactive elements, none of its forms with atomic masses from 85Tc to 120Tc are stable. Most of them undergo a beta+ decay to molybdenum. The technetium-98 radioisotope decays into ruthenium-98 through beta decay. With a half-life of 4.21 million years, the 97Tc isotope is the longest-lived isotope of technetium. 

 

The 97Tc and 99Tc isotopes of technetium are not only the first isolated forms but also the first synthetically produced isotopes of any chemical element. According to the chemical calculation, there are 2.5×10−13 grams of 99Tc per gram of pitchblende. 

 

Main isotopes of technetium 

Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
95mTc syn 61 d ε 95Mo
γ
IT 95Tc
96Tc syn 4.3 d ε 96Mo
γ
97Tc syn 4.21×106 y ε 97Mo
98Tc syn 4.2×106 y β 98Ru
γ
99Tc trace 2.111×105 y β 99Ru

Source: Wikipedia

List of Technetium Compounds 

Technetium is able to form carbides, tellurides, selenides, sulfides, and oxides. In these chemical compounds, element 43 usually adopts the common oxidation states of +4, +5, and +7. 

 

The following is a list of the most commonly prepared technetium compounds, but none of them have a significant commercial use:


  • Bectumomab (mononucleal antibody)
  • Besilesomab (mononucleal antibody)
  • Technetium (99mTc) etarfolatide
  • Technetium (99mTc) fanolesomab
  • Technetium (99mTc) mebrofenin
  • Technetium (99mTc) nofetumomab merpentan
  • Technetium (99mTc) pintumomab
  • Technetium hexafluoride
  • Technetium trichloride
  • Technetium(IV) bromide
  • Technetium(IV) chloride
  • Technetium(VII) oxide
  • Pertechnetate ion TcO4
  • Pertechnetic acid

5 Interesting Facts and Explanations

  1. Technetium is the first artificially made chemical element of the periodic table that was predicted by Mendeleev but could not be found in any of Earth’s layers. The chemists were unable to find it in nature because the isotopes of technetium have a significantly shorter half-life in comparison to the age of our planet. For this reason, if there ever were some quantity of element 43 present in nature, it has decayed long since it’s occurrence. 
  2. It has been observed that the longest living isotope of technetium has a half-life of more than 4 million years. 
  3. The chemist Emilio Segrè has discovered the elements astatine and technetium. This scientific discoverer of Italian-American origin won the Nobel Prize in Physics in 1959 for the discovery of the antiproton, which is a subatomic antiparticle.
  4. Promethium and technetium are the only two chemical elements with Z<83 that have no stable isotopes.
  5. The Manganese family of elements contains the transition metals manganese (Mn), technetium (Tc), rhenium (Re), and bohrium (Bh).