Question

The polarising power of \[{\rm{B}}{{\rm{e}}^{2 + }}\]is nearly same as that of:
A. \[{\rm{B}}{{\rm{a}}^{2 + }}\]
B. \[{\rm{M}}{{\rm{g}}^{2 + }}\]
C. ${\rm{A}}{{\rm{l}}^{3 + }}$
D. ${{\rm{B}}^{3 + }}$

Answer 1

Hint: We know that cation refers to the ion bearing a positive charge. It means a cation is electron deficient by nature and has an affinity to electrons. We also know that, in a periodic table, some elements show diagonal relationship.

Complete Step by step answer: Polarising power: The polarising power of any cation or anion is dependent on the charge density of cation or anion. If we consider a cation i.e. an ion bearing a positive charge, then the charge density refers to the ability of that ion to attract valence electrons from the nearest anion i.e. the ion bearing a negative charge due to excess of electrons.
The comparative analysis of polarising power of a cation is done on the basis of Fajan’s rule and the size of the cation. Fajan’s rule of polarisation explains about the covalent character developed by the ionic compound. According to it, the charge on the cation is directly proportional to the polarising power i.e. greater the charge on cation means greater will be its polarising power. Along with this the polarising power depends upon the size of the cation i.e. smaller the size of the cation more will be its polarising power as a small cation possesses more charge density. The given cation \[{\rm{B}}{{\rm{e}}^{2 + }}\] will have a polarising power similar to the cation ${\rm{A}}{{\rm{l}}^{3 + }}$. This is because the elements forming these cations i.e. beryllium and aluminium show resemblance due to diagonal relationship.

Hence, option (C) ${\rm{A}}{{\rm{l}}^{3 + }}$, is the correct option.

Note: It should be noted that due to the diagonal relationship between the elements forming the cation \[{\rm{B}}{{\rm{e}}^{2 + }}\] and ${\rm{A}}{{\rm{l}}^{3 + }}$ i.e. beryllium and aluminium respectively the cations will have the similar polarising power.
it depends how easily they are able to create a polarity in between the two atoms in a bond.