Revision Guide • Class 10-12 / JEE / NEET
Technetium (Tc)
By Periodic Table India
CBSE / JEE Prep Notes
Chemistry Elements Transition Metals Radioactivity JEE NEET CBSE ICSE
Introduction
Technetium (Tc) is a chemical element with atomic number 43. It is unique as the lightest element in the periodic table that has no stable isotopes, making all of its isotopes radioactive. Technetium is categorized as a heavy element primarily due to its atomic mass and is considered rare because it occurs naturally only in trace quantities (as a product of spontaneous fission of uranium or neutron capture by molybdenum) and is primarily produced synthetically. Its scarcity and inherent radioactivity limit its widespread common applications.
Periodic Table Placement
- Atomic Number (Z): 43
- Group: 7 (Transition metals, often referred to as the Manganese group)
- Period: 5
- Block: d-block
- Electronic Configuration:
[Kr] 4d⁵ 5s²- Full configuration:
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁵ 5s²
- Full configuration:
Radioactivity & Stability
Technetium is a wholly radioactive element; it has no stable isotopes.
- Most Stable Isotopes:
- $^{98}\text{Tc}$: Half-life of
4.2 × 10⁶years. Decays via beta-minus (β⁻) emission to $^{98}\text{Ru}$. - $^{99}\text{Tc}$: Half-life of
2.11 × 10⁵years. Decays via beta-minus (β⁻) emission to $^{99}\text{Ru}$. This is the most prevalent isotope resulting from nuclear fission.
- $^{98}\text{Tc}$: Half-life of
- Metastable Isotope of Significance:
- $^{99\text{m}}\text{Tc}$ (Technetium-99m): Half-life of
6.01hours. Decays by isomeric transition (gamma emission) to the ground state $^{99}\text{Tc}$. This isotope is critical in nuclear medicine due to its short half-life and pure gamma emission (no particulate radiation), which minimizes patient dose.
- $^{99\text{m}}\text{Tc}$ (Technetium-99m): Half-life of
- Type of Decay: Primarily beta-minus (β⁻) emission for its longer-lived isotopes, and gamma emission (isomeric transition) for the metastable $^{99\text{m}}\text{Tc}$. No naturally occurring alpha decay isotopes are significant for Tc.
Scientific Importance
Technetium’s importance stems almost entirely from its synthetic production and radioactive properties.
- Synthetic Production: Technetium was the first artificially produced element, discovered in 1937 by Emilio Segrè and Carlo Perrier after bombarding molybdenum with deuterium nuclei in a cyclotron. It is now largely produced as a fission product of uranium-235 in nuclear reactors.
- Research Uses & Applications:
- Nuclear Medicine: $^{99\text{m}}\text{Tc}$ is the most widely used radioisotope in diagnostic nuclear medicine. Its properties (short half-life, emission of low-energy gamma rays (140 keV) which can be detected by gamma cameras, and ability to form various biologically active compounds) make it ideal for imaging soft tissues, bones, heart, brain, and other organs.
- Corrosion Inhibition: Pertechnetate ion ($\text{TcO}_4^-$) is a powerful corrosion inhibitor for steel. However, its radioactive nature limits its practical application in this role to closed systems or specialized research.
- Radiotracers: Used as tracers in various chemical and biological research due to its detectable radioactivity.
- Lack of Common Applications: Due to its inherent radioactivity, high production cost, and short half-lives of most isotopes, Technetium has virtually no bulk commercial applications outside of specialized medical and research fields.