Question

The extra stability of half-filled subshell is due to
(A) Symmetrical distribution of electrons
(B) Smaller coulombic repulsion energy
(C) The presence of electrons with the same spin in non-degenerate orbitals
(D) Larger exchange energy
(E) Relatively smaller shielding of electrons by one another
Identify the correct statements

• A. (B), (D) and (E) only
• B. (A), (B), (D) and (E) only
• C. (B), (C) and (D) only
• D. (A), (B) and (D) only

Hint:

The enhanced stability of half-filled and fully filled subshells arises from a combination of factors related to electron arrangement and interactions. Symmetrical distribution minimizes repulsion and can slightly affect shielding, while maximized exchange energy provides a significant stabilizing effect.

Answer 1

The Correct Option is B

The question is about the extra stability of a half-filled subshell in atoms, which is a key concept in chemistry, specifically in understanding electronic configurations and atomic structure.

1. Symmetrical distribution of electrons (Option A): Half-filled subshells have a symmetrical distribution of electrons. This symmetry contributes to stability because it leads to a more even shape of the electron cloud, which minimizes repulsion between electrons.
2. Smaller coulombic repulsion energy (Option B): In a half-filled subshell, electrons are spread out evenly across the orbital, reducing the repulsion between them as much as possible. This reduced repulsion results in lower energy and hence, greater stability.
3. Larger exchange energy (Option D): Exchange energy is a quantum mechanical concept where electrons in degenerate orbitals (same energy) can exchange positions. It reduces the energy of the atom, particularly in half-filled cases, as this exchange happens most frequently. Thus, it increases stability.
4. Relatively smaller shielding of electrons by one another (Option E): In a half-filled configuration, electrons are more evenly distributed across the orbital. This reduces the shielding effect, where inner electrons block the outer electrons from the nucleus. The reduced shielding enhances the nuclear attraction on outer electrons, stabilizing the atom further.

Therefore, the correct statements are (A), (B), (D), and (E), matching the given correct answer: (A), (B), (D), and (E) only.

Answer 2

Step 1: Understand the reasons for the extra stability of half-filled subshells.
(A) Symmetrical distribution of electrons: This leads to a more balanced and stable arrangement.
(B) Smaller coulombic repulsion energy: Symmetrical distribution increases the average distance between electrons, reducing repulsion.
(C) The presence of electrons with the same spin in non-degenerate orbitals: This describes Hund's rule, which is followed but isn't the primary extra stability factor compared to other partially filled cases also obeying Hund's rule.
(D) Larger exchange energy: Maximized exchange of electrons with the same spin in degenerate orbitals releases energy and increases stability.
(E) Relatively smaller shielding of electrons by one another: In a symmetrically distributed half-filled or fully filled subshell, the electrons are more evenly spread out. This can lead to a slightly more effective nuclear charge experienced by each electron compared to an asymmetrically filled subshell where some electrons might be closer and cause more shielding for others. While the effect might be subtle, it contributes to the overall stability.
Step 2: Identify the correct statements.
The primary reasons for the extra stability are symmetrical distribution (A), reduced coulombic repulsion (B), maximized exchange energy (D), and a slightly more effective nuclear charge due to reduced uneven shielding (E).
Step 3: Choose the option containing the correct statements.
The option containing statements (A), (B), (D), and (E) is (2).