Question

Account for the following:
$SnC{{l}_{4}}$ is more covalent than $SnC{{l}_{2}}$.

Answer 1

Calculate the oxidation number possessed by Sn in both the compounds.
- We know that the polarisation ability of cation is related to the charge possessed by a cation.

Complete Solution :
So in the question it is asked that, if we compare the two compounds, $SnC{{l}_{4}}$ and $SnC{{l}_{2}}$, which one shows more covalent nature.
- We know that, in many cases, many ionic bonds present in ionic compounds are not purely ionic; it may show slight covalent nature also and vice versa.
- We also know that a polar covalent bond more stable that the pure covalent bond and ionic bond
The Fajan’s rule that is related to the covalent and ionic nature of the compounds suggested that the stability of the polar covalent bond depends on the polarizing power of the cation present in the compounds and also on the polarisability of the anion.
- This rule that accounts for polarization is called the Fajan’s rule for polarization, and he has set some postulates that support this rule. Let’s briefly discuss the conditions that may enhance the covalent nature of the compound.

1. If the cation is having smaller atomic radii then they will possess high polarizing ability i.e. they could distort the electron cloud to a greater extent. Hence as the cationic size decreases covalent nature increases.
2. If the anion is having greater size, then its polarisability will be more. The electronic cloud possessed by the larger anion gets deformed easily by the cation. Hence larger the anionic size, the molecule will have covalent nature.
3. The polarisability of anion by the cation increases as there will be an increase in the charge of anions, cations or in both of them.
4. The cations that possess pseudo electronic configuration will have greater polarizing power but with noble gas configuration has less polarizing ability.
   - Now let’s discuss for the solution, here we know the anions related to both the compounds $SnC{{l}_{4}}$ and $SnC{{l}_{2}}$ are similar, the chlorine ion $\left( C{{l}^{-}} \right)$.
   So the deciding factor here is the charge possessed by the cation and the cationic size.
   In $SnC{{l}_{4}}$, the Sn possess$+4$ charge and in $SnC{{l}_{2}}$ it is $+2$.Hence $SnC{{l}_{4}}$ has the greater polarisability i.e. it polarizes the electron cloud of neighboring atom to a greater extend and will possess greater covalent name.
   We also know that, $S{{n}^{4+}}$ possess smaller cationic radii than the $S{{n}^{2+}}$, hence $SnC{{l}_{4}}$ is more covalent in nature.

Note: $SnC{{l}_{2}}$ could be said as an ionic compound.
Polarization- The ability of the positively charged ion, the cation to distort the electron cloud is called the polarization power.
Polarisability- It is the tendency of the anion to get polarized by the cation.