Question

The polarising action of $C{d}^{2+}$ ion over anions is stronger than that of $C{a}^{2+}$ because:

• A. The charges of the ions are same
• B. Their radii are similar $(C{a}^{2+}=0.104\text{nm};C{d}^{2+}=0.099\text{nm})$
• C. $C{a}^{2+}$ ion has a noble gas electronic configuration and the $C{d}^{2+}$ ion has a 18$e^{-}$ electronic configuration in the outer shell
• D. All the above are correct

Answer 1

The correct option is C $C{a}^{2+}$ ion has a noble gas electronic configuration and the $C{d}^{2+}$ ion has a 18$e^{-}$ electronic configuration in the outer shell

${}_{20}Ca:\left[Ar\right]4s^2$
$C{a}^{2+}:\left[Ar\right]\to$ noble gas configuration
${}_{48}Cd:\left[Kr\right]5s^{2}4d^{10}$
$C{d}^{2+}:\left[Kr\right]4d^{10}$
or,
$C{d}^{2+}:1s^{2}2s^{2}2p^{6}3s^{2}3p^6\underset{-}{4s^2}3d^{10}\underset{-}{4p^6}\underset{-}{4d^{10}}$
$2+6+10=18$
$C{d}^{2+}:\left[Kr\right]4d^{10}\to$ 18$e^{-}$ electronic configuration

The outer most d-orbital cannot shield the nuclear charge as much and hence, the polarisation of $C{d}^{2+}>C{a}^{2+}$.