Al and Ga have nearly the same covalent radii because of

Options

A. greater shielding effect of s-electrons of Ga atoms
B. poor shielding effect of s-electrons of Ga atoms
C. poor shielding effect of d-electrons of Ga atoms
D. greater shielding effect of d-electrons of Ga atoms.

Explanation

To solve the question of why aluminum (Al) and gallium (Ga) have nearly the same covalent radii, we need to analyze the electronic configurations and the effects of shielding in these elements.

### Step-by-Step Solution:

1. **Identify the Electronic Configurations:**
- Aluminum (Al) has the electronic configuration: \( \text{Ne} \, 3s^2 \, 3p^1 \).
- Gallium (Ga) has the electronic configuration: \( \text{Ar} \, 3d^{10} \, 4s^2 \, 4p^1 \).

2. **Understand the Concept of Shielding:**
- Shielding refers to the phenomenon where inner electrons repel outer electrons, reducing the effective nuclear charge felt by the outer electrons.
- The effectiveness of shielding varies with the type of orbital. Generally, s and p orbitals provide better shielding than d and f orbitals.

3. **Analyze the Impact of d Orbitals in Gallium:**
- Gallium has a filled 3d subshell (10 electrons). The presence of these d electrons leads to poor shielding compared to s and p electrons.
- This poor shielding results in a higher effective nuclear charge experienced by the outer electrons in gallium, which pulls them closer to the nucleus.

4. **Compare Atomic Radii:**
- Although gallium has an additional shell (4th shell) compared to aluminum (3rd shell), the poor shielding effect of the d electrons in gallium counterbalances the increase in atomic radius that would typically occur due to the addition of a new shell.
- As a result, the covalent radii of aluminum and gallium end up being nearly the same.

5. **Conclusion:**
- The nearly identical covalent radii of Al and Ga can be attributed to the poor shielding effect of the d electrons in Ga, which increases the effective nuclear charge and leads to a contraction in atomic size.

### Final Answer:
Al and Ga have nearly the same covalent radii because of the poor shielding effect of d electrons in gallium, which counterbalances the increase in atomic size due to the addition of a new shell.