Gallium has smaller atomic radius than aluminium because of

Options

A. Poor shielding power of `d` electrons of `Ga` atom
B. Poor shielding power of `s` electrons of `Ga` atom
C. Greater shielding power of `s` electrons of `Al` atom
D. Greater shielding power `d` electrons of `Ga atom.

Answer

To explain why gallium has a smaller atomic radius than aluminum, we can break down the reasoning into several steps:

### Step 1: Understand Atomic Radius
The atomic radius is the distance from the nucleus of an atom to the outermost shell of electrons. It can be influenced by the number of electron shells and the effective nuclear charge experienced by the outermost electrons.

### Step 2: Compare Electronic Configurations
- **Aluminum (Al)**: The electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^1\).
- **Gallium (Ga)**: The electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^1\).

### Step 3: Analyze the Electron Shells
Both aluminum and gallium have their outermost electrons in the third and fourth energy levels, respectively. However, gallium has additional electrons in the 3d subshell.

### Step 4: Consider the Shielding Effect
The 3d electrons in gallium do not shield the nucleus effectively due to their poor shielding ability. This means that the effective nuclear charge felt by the outer electrons in gallium is higher than that in aluminum.

### Step 5: Evaluate the Coulombic Attraction
The increased effective nuclear charge in gallium leads to a stronger Coulombic attraction between the nucleus and the outermost electrons, causing the atomic radius to contract.

### Conclusion
Thus, gallium has a smaller atomic radius than aluminum because the presence of the 3d electrons in gallium leads to a poor shielding effect, resulting in a higher effective nuclear charge and a stronger attraction between the nucleus and the outermost electrons.