Question

Which of the following is correct about the stability of half-filled and completely filled subshells?
(i) Relatively small shielding
(ii) Larger coulombic repulsion energy
(iii) Smaller exchange energy
(iv) Smaller coulombic repulsion energy
(v) Larger exchange energy

• A. (i), (ii) and (iii)
• B. (i), (iii) and (v)
• C. (i), (iv) and (v)
• D. (ii), (iii) and (v)
• E. (i), (ii) and (iv)

Hint:

Half-filled and completely filled subshells are highly stable due to their larger exchange energy and lower coulombic repulsion, making them energetically favorable.

Answer 1

The Correct Option is C

- Relatively small shielding (i): This is true for half-filled and completely filled subshells. Due to the symmetric distribution of electrons, these configurations are more stable, leading to small shielding effects.
- Larger coulombic repulsion energy (ii): This is incorrect. For half-filled or completely filled subshells, the electrons are arranged symmetrically, reducing repulsion and making the system more stable.
- Smaller exchange energy (iii): This is incorrect. A half-filled or fully filled subshell has more exchange energy, which contributes to stability. This is why configurations like \( \text{d}^5 \) and \( \text{p}^6 \) are particularly stable.
- Smaller coulombic repulsion energy (iv): This is correct. Due to electron pairing and symmetric arrangement, there is less repulsion between electrons, leading to lower coulombic repulsion energy. - Larger exchange energy (v): This is correct. The exchange energy is maximized in half-filled and fully filled subshells, contributing to the stability of these configurations.
Thus, the correct answer is (C) (i), (iv), and (v). These are the characteristics of half-filled and fully filled subshells that make them particularly stable.