Nature of bonding found in vapour phase `AlCl_3` is

Options

A. only covalent
B. Covalent & ionic
C. Covalent & coordinate
D. Only ionic

Answer

To determine the nature of bonding in the vapor phase of \( \text{AlCl}_3 \), we can follow these steps:

### Step 1: Understand the Structure of \( \text{AlCl}_3 \)
- \( \text{AlCl}_3 \) consists of aluminum (Al) and chlorine (Cl). In the solid state, \( \text{AlCl}_3 \) forms an ionic lattice structure due to the ionic nature of the bond between the aluminum cation (\( \text{Al}^{3+} \)) and chloride anions (\( \text{Cl}^- \)).

### Step 2: Analyze the Bonding in Vapor Phase
- In the vapor phase, \( \text{AlCl}_3 \) does not exist as isolated ions. Instead, it tends to form dimers, specifically \( \text{Al}_2\text{Cl}_6 \). This dimerization indicates that the bonding in the vapor phase is not purely ionic.

### Step 3: Consider Electronegativity
- The electronegativity of chlorine is approximately 3.16, while that of aluminum is around 1.61. The difference in electronegativity is significant, but since we are considering the vapor phase, we need to analyze the character of the bonds formed.

### Step 4: Polarization Effects
- The \( \text{Al}^{3+} \) ion has a high charge density due to its small size and high charge (+3). This high charge density allows it to polarize the larger \( \text{Cl}^- \) ions effectively. The polarization of the chloride ions by the aluminum cation contributes to the covalent character of the bonds in the vapor phase.

### Step 5: Conclusion
- In the vapor phase, \( \text{AlCl}_3 \) exhibits covalent character due to the formation of dimers and the significant polarization effects of the aluminum cation on the chloride anions. Therefore, the nature of bonding in the vapor phase of \( \text{AlCl}_3 \) is predominantly covalent.

### Final Answer
The nature of bonding found in the vapor phase of \( \text{AlCl}_3 \) is **covalent**.

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