Introduction to Technetium
Technetium (Tc) is a fascinating chemical element, unique among lighter elements as it is the lightest element with no stable isotopes. All isotopes of Technetium are radioactive, meaning they undergo radioactive decay. Its atomic number is 43. The name “Technetium” originates from the Greek word “technetos,” meaning artificial, reflecting its initial discovery through synthesis rather than natural isolation.
Basic Information
| Property | Value |
|---|---|
| Element Symbol | Tc |
| Atomic Number (Z) | 43 |
| Atomic Mass (most stable isotope, Tc-99) | 98.9062 u |
| Group | 7 |
| Period | 5 |
| Block | d-block |
| Category | Transition Metal |
Occurrence and Significance
Technetium is extremely rare in the Earth’s crust, primarily produced artificially in nuclear reactors. A tiny amount is formed as a spontaneous fission product of uranium and thorium. Its most significant application is in nuclear medicine, particularly the metastable isotope Technetium-99m (⁹⁹ᵐTc). This isotope is widely used in diagnostic imaging, such as bone scans, cardiac stress tests, and kidney scans, due to its short half-life and suitable gamma emission properties. Hospitals and diagnostic centers across India, including those in major cities like Mumbai, Delhi, and Chennai, frequently utilize ⁹⁹ᵐTc for medical imaging procedures.
Atomic Structure of Technetium
Understanding the atomic structure of Technetium involves identifying the fundamental subatomic particles: protons, neutrons, and electrons, and describing how electrons are arranged within the atom.
Protons, Neutrons, and Electrons
For a neutral atom of Technetium, specifically considering its most stable and common isotope, Technetium-99 (⁹⁹Tc):
- Atomic Number (Z): The atomic number of an element determines the number of protons in the nucleus. For Technetium, Z = 43.
- Number of Protons = 43
- Number of Electrons: In a neutral atom, the number of electrons is equal to the number of protons to balance the positive charge of the nucleus.
- Number of Electrons = 43
- Number of Neutrons: The mass number (A) represents the total number of protons and neutrons in the nucleus. For Technetium-99, A = 99. The number of neutrons is calculated as A - Z.
- Number of Neutrons = 99 (Mass Number) - 43 (Atomic Number) = 56
Therefore, a neutral atom of Technetium-99 contains 43 protons, 56 neutrons, and 43 electrons.
Electron Configuration
The electron configuration describes the distribution of electrons of an atom or molecule in atomic orbitals. For Technetium (Z=43), the electrons fill the orbitals according to the Aufbau principle, Hund’s rule, and Pauli exclusion principle.
The full electron configuration for Technetium is: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁵
Using the noble gas shorthand notation, which represents the core electrons by the symbol of the preceding noble gas (Krypton, Kr, with 36 electrons), the configuration becomes: [Kr] 4d⁵ 5s²
This indicates that after the electron configuration of Krypton, there are 2 electrons in the 5s subshell and 5 electrons in the 4d subshell.
Valence Electrons
Valence electrons are the electrons in the outermost shell of an atom and are primarily involved in chemical bonding. For transition metals like Technetium, both the electrons in the outermost ‘s’ subshell and the partially filled ‘d’ subshell of the principal quantum number just below the outermost ‘s’ subshell are considered valence electrons.
In Technetium’s electron configuration [Kr] 4d⁵ 5s²:
- The outermost principal energy level is n=5 (the 5s subshell).
- The partially filled d subshell is 4d.
Therefore, the valence electrons for Technetium are the 2 electrons in the 5s orbital and the 5 electrons in the 4d orbital. Total Valence Electrons = 2 (from 5s) + 5 (from 4d) = 7
This count of 7 valence electrons is consistent with Technetium being in Group 7 of the periodic table.