Question

LiCl is covalent while NaCl is ionic. Answer whether the above statement is true or false.

Answer 1

Hint: Ionic compounds are composed of one metal and one non-metal. The ionic compound has an ionic character. The ionic compound can have some covalent character also. The extent of a covalent character depends upon the polarizing power of cation and polarizability of the anion.

Complete answer
The bond between metal and non-metal is known as an ionic bond and the compound is known as an ionic compound. Lithium and sodium are metal and chlorine are non-metal, so lithium chloride and sodium chloride both are ionic compounds.

Lithium chloride is an ionic compound but it also has some covalent character due to the very small size of lithium metal.

The covalent character in ionic compounds is determined by using Fajan’s rule. According to Fajan’s rule, the covalent character in ionic compounds is directly proportional to the polarizing power of the cation and inversely proportional to the polarizability of the anion.

- The polarizing power of the cation is high if the size is small and the charge is maximum.
- Polarizing power of the cation $ \propto $ Charge on cation.
- Polarizing power of the cation $ \propto $ $\dfrac {1}{size\, of \,cation}$.
- The polarizability of the anion will be high if the size is large and the charge is maximum.
- Polarizability of the anion $ \propto $ size of anion.
- Polarizability of the anion $ \propto $ Charge on anion.
- Lithium is of the smallest size in group-I so, its polarizing power is very high so it has a covalent character.

Therefore, the statement, LiCl is covalent while NaCl is ionic is true.

Note: Ionic compounds have ionic bonds and covalent compounds have covalent bonds. The covalent compounds are made up of non-metals only. Fajan’s rule determines the covalent character in the ionic bond only, not the ionic character in the covalent bond. The covalent character is directly proportional to the solubility in non-polar solvents and inversely proportional to the solubility in the polar solvent.