Question

The lesser covalency of $FeC{{l}_{2}}$ over $FeC{{l}_{3}}$ is due to:
A. lower polarizing power of $F{{e}^{+2}}$ than that of $F{{e}^{+3}}$ Ion
B. lower polarizing power of $F{{e}^{+3}}$ than that of $F{{e}^{+2}}$
C. higher polarizability of $F{{e}^{+3}}$ than $F{{e}^{+2}}$
D. higher polarizability of $F{{e}^{+2}}$ than $F{{e}^{+3}}$

Answer 1

The properties of d block elements as well as Fajan’s rule is to be used to solve this question. Size of $F{{e}^{+2}}>F{{e}^{+3}}$, use this information along with the Fajan’s rule to find out the conclusion.

Complete Solution :
- In order to answer our question, we need to learn about the properties of the d block elements. As the charge on the nucleus increases which accompanies the filling of the inner d orbitals the ionisation enthalpy along each series of the transition elements increases from left to right. However many small variations occur. Values of the nuclear charge show that the enthalpies of these elements do not increase as steeply as the main group elements do. Although the 1st ionisation enthalpy, in general, increases, the magnitude of the increase in the 2nd and 3rd ionisation enthalpy for the successive elements, in general, is much higher. There is thus a reorganisation energy accompanying ionisation with some gains in exchange energy as the number of electrons increases and from the transference of s electron into d orbital. There is generally expected increasing trend in the values as the effective nuclear charge increases
- However, the answer can be explained on the basis of Fajan’s Rule. Polarising power decreases, as size of cation decreases and covalent character reduces too. And we know that the size of $F{{e}^{+2}} > F{{e}^{+3}}$. So, the correct answer is “Option A”.

Note: The d block elements are also called transition elements as they have d orbitals that are not completely filled in ground state as well as the oxidation state. But, as Zn, Cd and Hg have full ${{d}^{10}}$ configuration, they are not counted as transition elements.