Question

The atomic sizes of $Ga$ and $Al$ are almost the same because:

• A. Poor shielding effect of the electrons in $d$ orbitals
• B. More shielding effect of $d$ electrons
• C. Poor shielding effect of $f$ orbitals in gallium
• D. High screening effect of $3s,3pand3d$ electrons.

Answer 1

The correct option is A Poor shielding effect of the electrons in $d$ orbitals

The electronic configuration of $Ga$
$\left[Ar\right]3d^{10}4s^{2}4p^1$
Due to the poor shielding effect of $d$ electrons, the screening effect (or shielding effect ) decreases for the outermost electrons. As a result, the effective nuclear charge on the outer electrons increases, which results in decrease in its size. Hence, $GaandAl$ are almost same in size.
The penetration power of the orbitals is in the order : $s>p>d>f$ .
So, if the inner electrons are present in $s$ orbital, they are going to have a large screening effect, compared to the ones present in $p$-orbital, weakening the screening effect.