Question

Among \[{\text{LiCl}}\] , \[{\text{BeC}}{{\text{l}}_2}\] , \[{\text{BC}}{{\text{l}}_3}\] and \[{\text{CC}}{{\text{l}}_4}\], the covalent bond character follows the order:
A. \[{\text{LiCl < BeC}}{{\text{l}}_{\text{2}}}{\text{ < BC}}{{\text{l}}_{\text{3}}}{\text{ < CC}}{{\text{l}}_{\text{4}}}\]
B. \[{\text{BC}}{{\text{l}}_{\text{3}}}{\text{ < CC}}{{\text{l}}_{\text{4}}} < {\text{BeC}}{{\text{l}}_{\text{2}}} < {\text{LiCl}}\]
C. \[{\text{BeC}}{{\text{l}}_{\text{2}}}{\text{ < LiCl < CC}}{{\text{l}}_{\text{4}}} < {\text{BC}}{{\text{l}}_{\text{3}}}\]
D. \[{\text{CC}}{{\text{l}}_{\text{4}}} < {\text{BC}}{{\text{l}}_{\text{3}}} < {\text{BeC}}{{\text{l}}_{\text{2}}} < {\text{LiCl}}\]

Answer 1

Hint: Covalent character of an ionic compound can be explained on the basis of Fajan’s rules.
The covalent character of an ionic compound is directly proportional to the polarization or the distortion of the electron cloud of the anion by the cation.

Complete step by step:
The ability of an ion to distort the electron cloud of another ion is called its polarizing power and the tendency of an ion to get distorted by the other ion is called its polarizability.
As the size of an anion is larger than a cation and the electrons in an anion are less tightly bound to the nucleus, an anion possesses high polarizability.
According to the Fajan’s rules, the factors affecting the magnitude of polarizing power of a cation are as follows.
High charge on the cation: More the charge on a cation, more is the polarizing power of the cation.
Small size of the cation: Smaller the size of a cation, greater will be its attraction for the electrons of the anion. Thus, greater will be its polarizing power. Consequently, greater will be its covalent character.
Electronic configuration of cation: In case of cations having same charge and almost same size, the cations having pseudo inert gas configuration will $\left( {{\text{n}}{{\text{s}}^{\text{2}}}{{\text{p}}^{\text{6}}}{{\text{d}}^{10}}} \right)$ have more polarizing power than those having inert gas configuration $\left( {{\text{n}}{{\text{s}}^{\text{2}}}{{\text{p}}^{\text{6}}}} \right)$ .
Now, \[{\text{LiCl}}\] , \[{\text{BeC}}{{\text{l}}_2}\] , \[{\text{BC}}{{\text{l}}_3}\] and \[{\text{CC}}{{\text{l}}_4}\] are chlorides of different elements with different positive charges on them. Lithium in \[{\text{LiCl}}\] has +1 charge, beryllium in \[{\text{BeC}}{{\text{l}}_2}\] has +2 charge, boron in \[{\text{BC}}{{\text{l}}_3}\] has +3 charge and carbon in \[{\text{CC}}{{\text{l}}_4}\] has +4 charge.
In these chlorides, since the magnitude of the positive charge on the cation increases from +1 to +4, the polarizing power of these cations to polarize chloride ion increases as \[{\text{L}}{{\text{i}}^ + }{\text{ < B}}{{\text{e}}^{2 + }}{\text{ < }}{{\text{B}}^{3 + }}{\text{ < }}{{\text{C}}^{4 + }}\]. Thus, the covalent character of these chlorides also increases in the same order as \[{\text{LiCl < BeC}}{{\text{l}}_{\text{2}}}{\text{ < BC}}{{\text{l}}_{\text{3}}}{\text{ < CC}}{{\text{l}}_{\text{4}}}\]. So, the correct option is A.

Note: The factors affecting the polarizability of an anion are as follows.
High charge on the anion: As the magnitude of the negative charge on an anion increases, the polarizability of the anion also increases. In other words, more the charge on the anion, more is the polarizability of the anion.
Large size of the anion: Larger the size of an anion, less tightly its electrons will be held by the nucleus. Hence, larger anions can be polarized more easily.