Question

Which of the following Pairs of ions have the same electronics configuration?
A. $C{{u}^{2+}},C{{r}^{2+}}$
B. $F{{e}^{3+}},M{{n}^{2+}}$
C. $C{{o}^{3+}},N{{i}^{3+}}$
D. $S{{c}^{3+}},C{{r}^{3+}}$

Answer 1

Hint: The polarising power of a cation is described as its ability to pull the electron cloud towards itself. The polarising power of a cation is its ability to distort the electron cloud of an anion. The polarising power of a cation is expressed by the symbol known as phi or $\Phi $ and it is referred to as the ionic potential. The ratio of charge on the cation to that of radius of the cation is equal to the value of $\Phi $ for that cation.

Complete step by step answer:
Here, different pairs of cations are given containing cations of alkali earth metals and alkaline earth metals. Sodium, lithium and rubidium are alkali metals whereas magnesium and aluminium are alkaline earth metals. As these all elements are metals, they lose electrons to form cations. When these cations form an ionic compound with anions, they try to pull an ion's electron cloud towards itself but repel the positive nucleus of that anion.
This results in the deformation of electron clouds of anion by the cation which is described as the polarising power of the cation. Let us compare the polarising power of a pair of cations given in each option to identify the correct answer.
In option (B), the pair of cations given consists of and ions. Though $F{{e}^{3+}},M{{n}^{2+}}$ is categorized as the alkali metals in the periodic table, it shows many similarities with the alkaline earth metal, magnesium. This is because the diagonal relationship between iron and magnesium. It is assumed that there is an existence of a diagonal relationship between the pair of elements belonging to the second and third period of the Periodic table. These pairs of elements exhibit resemblance in their properties. On moving diagonally in the Periodic table, the ratio of charge on the cations of the elements and the cationic radius is almost the same (The value of ionic radius for and are \[60\] and \[65pm\] respectively.).

Therefore, the value of polarising power of and ions will be almost the same. Hence, option (B) is correct.

Note: A polarising power is a characteristic of a cation whereas polarizability is a term used in the context of an anion. Both polarising power and polarizability are different terms. Polarizability of an anion is the ability of anion to become polarized by the cation. The polarizability of anions with large size will be large and hence, the electron cloud of that anion will distort easily by cation. Also, as the charge on the anion increases, the polarizability will also increase.