Question

The properties of most of the ionic solids deviate from their ideal ionic character because the lattice undergoes some distortion. Cations are usually smaller than anions and have a higher effective nuclear charge. The outer electron cloud in a cation is more firmly held than in an anion. The loose electron cloud of an anion, when attracted by the electron cloud of a cation, gets distorted. This phenomenon is known as polarization. Due to this phenomenon, the electron cloud of an anion shifts towards the cation which decreases both the magnitude of positive charge on the cation and the negative charge on the anion. In other words, covalent character develops in the ionic bond.

Amongst $LiCl$, $RbCl$, $BeC{l}_2$ and $MgC{l}_2$ the compounds with the greatest and the least ionic character respectively are:

• A. $LiCl$ and $RbCl$
• B. $RbCl$ and $MgC{l}_2$
• C. $RbCl$ and $BeC{l}_2$
• D. $MgC{l}_2$ and $BeC{l}_2$

Answer 1

The correct option is C $RbCl$ and $BeC{l}_2$

According to Fajan's rule, smaller the cation and higher the charge on it more will be the covalent character (thus less ionic character). Amongst the cations in the given compounds, $B{e}^{2+}$ is the smallest and $R{b}^{+}$ is the largest cations. Thus, $RbCl$ has the least and $BeC{l}_2$ has the most covalent character among the given compounds.