Question

Among the following the maximum covalent character is shown by the compound: (a) \(\mathrm{MgCl}_{2}\) (b) \(\mathrm{FeCl}_{2}\) (c) \(\mathrm{AlCl}_{3}\) (d) \(\mathrm{SnCl}_{2}\)

Short answer

The compound with maximum covalent character is \(\mathrm{AlCl}_{3}\).

Step-by-step solution

Understand Covalent Character

Covalent character in ionic compounds is determined by the distortion of the electron cloud of the anion by the cation, also known as polarization. The Fajans' rule states that for high covalent character: the cation should be small and highly charged, and the anion should be large and highly charged.

Analyze the Cations

Evaluate each cation from the given options: - Mg in \(\text{MgCl}_2 \) is a \(\text{Mg}^{2+}\) ion.- Fe in \(\text{FeCl}_2\) is a \(\text{Fe}^{2+}\) ion.- Al in \(\text{AlCl}_3\) is a \(\text{Al}^{3+}\) ion.- Sn in \(\text{SnCl}_2\) is a \(\text{Sn}^{2+}\) ion.The Al cation has the highest charge (+3), which suggests a higher covalent character according to Fajans’ rule.

Analyze the Anion's Size

All the compounds contain chloride ions (\(\text{Cl}^-\)). Since the anion is the same in each case, our focus should be mainly on the cation's charge and size for polarization effect.

Compare Polarizing Powers

Considering both the charge and size of the cations, - \(\text{Al}^{3+}\) has a higher polarizing power than \(\text{Mg}^{2+}\), \(\text{Fe}^{2+}\), and \(\text{Sn}^{2+}\).According to Fajans' rule, \(\text{AlCl}_3\) would have the most covalent character due to the small size and high charge of \(\text{Al}^{3+}\).

Conclusion: Select the Compound

Given the higher charge and smaller size of the \(\text{Al}^{3+}\) ion, \(\text{AlCl}_3\) is expected to have the maximum covalent character among the options.

Key concepts

Fajans' Rule

Fajans' Rule helps us predict if a chemical bond has more ionic or covalent characteristics. It lays emphasis on the cation and anion involved in the bond and how their properties affect the bond's nature. Two main points of the rule are key:

• The cation should be small and possess a high positive charge.
• The anion should be large and carry a significant negative charge.

This rule suggests that the more polarizing a cation (due to its charge and size), the more covalent character the compound has. Applying this, AlCl₃ would have more covalent character because Al³⁺ is a small and highly charged cation.

Polarization of Anions

Polarization of anions occurs when the electron cloud of a negatively charged ion, or anion, is distorted due to the positive charge and proximity of a cation. This distortion makes the bond shift from being purely ionic towards possessing some characteristics of a covalent bond. The larger the anion and the higher the charge, the easier it is to polarize.

For example, in AlCl₃, the Cl⁻ ions are polarized by Al³⁺ due to the latter’s high charge and small size. This causes electrons to be shared rather than fully transferred, contributing to the covalent nature of the bond. Polarization is key in determining the covalent character in traditionally ionic compounds.

Ionic vs Covalent Bonds

Ionic bonds form between atoms when one atom donates electrons to another, resulting in oppositely charged ions that attract each other. Typically, they form between metals and non-metals. On the other hand, covalent bonds form when two atoms share electrons, which usually happens between non-metals.

The lines can blur, however, due to the presence of partial charges and polarization effects. Fajans’ Rule helps to predict these mixed characteristics by focusing on polarizing power. When a cation, like Al³⁺ in AlCl₃, strongly polarizes the bonded anion, ionic bonds exhibit covalent traits. Consider this as a spectrum rather than a clear division. AlCl₃, while nominally ionic, shows significant covalent characteristics due to the effects outlined above.