Question

Which of the following statements is wrong? (1) \Lambdanhydrous \(\Lambda 1 \mathrm{Cl}_{3}\) sublimes at \(180^{\circ} \mathrm{C}\). (2) The vapour of anhydrous \(\Lambda 1 \mathrm{Cl}_{3}\) contains dimer \(\mathrm{\Lambdal}_{2} \mathrm{Cl}_{6}\) (3) The dimeric structure of \(\mathrm{A} \mathrm{l}_{2} \mathrm{Cl}_{6}\) is retained in benzenc. (4) The dimeric \(\mathrm{Al}_{2} \mathrm{Cl}_{6}\) contain \(3 \mathrm{C}\). \(2 \mathrm{c}\) bonds.

Short answer

Statement (4) is wrong.

Step-by-step solution

- Analyze statement (1)

Statement (1) reads: 'Anhydrous \(\text{AlCl}_3\) sublimes at \(180^\text{C}\)'. Check if \(\text{AlCl}_3\) sublimes at this temperature. Indeed, anhydrous \(\text{AlCl}_3\) does sublime at around this temperature.

- Analyze statement (2)

Statement (2) reads: 'The vapor of anhydrous \(\text{AlCl}_3\) contains dimer \(\text{Al}_2\text{Cl}_6\)'. Check if \(\text{AlCl}_3\) forms a dimer in the vapor phase. This is true, as \(\text{AlCl}_3\) can form dimers \(\text{Al}_2\text{Cl}_6\) in the vapor phase.

- Analyze statement (3)

Statement (3) reads: 'The dimeric structure of \(\text{Al}_2\text{Cl}_6\) is retained in benzene'. Examine if the dimeric form remains intact in benzene. This statement is correct since \(\text{Al}_2\text{Cl}_6\) is known to retain its dimeric structure in nonpolar solvents like benzene.

- Analyze statement (4)

Statement (4) reads: 'The dimeric \(\text{Al}_2\text{Cl}_6\) contains \(3 \text{C} - 2 \text{C}\) bonds.' Investigate the bonding in \(\text{Al}_2\text{Cl}_6\). Each \(\text{Al}_2\text{Cl}_6\) dimer contains \(2 \text{Cl}\) bridges forming \(3 \text{C} - 2 \text{e}\) bonds. This statement is wrong.

Key concepts

Sublimation Temperature

Sublimation is the process where a substance transitions directly from a solid to a gas without passing through the liquid phase. Anhydrous aluminum chloride (AlCl3) is a good example of this phenomenon.
One of the notable characteristics of anhydrous AlCl3 is its sublimation temperature, which is around 180°C. This means that at this temperature, solid AlCl3 directly converts into a gas.
This property is crucial in many industrial processes where controlled vaporization of the compound is required. Due to the heat required for sublimation, those working with AlCl3 need to ensure proper temperature regulation to handle the compound safely and effectively.

Dimer Formation

In the context of chemistry, dimer formation refers to two identical molecules bonding together.
For aluminum chloride (AlCl3), this process happens frequently in the vapor phase, where two AlCl3 molecules combine to form Al2Cl6.
The result is a dimer, Al2Cl6, which is more stable in the gas phase than individual AlCl3 molecules. This stability arises from additional bonding interactions present in the dimer form.
Understanding dimer formation is essential because many chemical reactions and properties of substances like AlCl3 depend on whether they are in monomer or dimer form.

Chemical Structure Retention

Chemical structure retention refers to the ability of a compound to maintain its molecular arrangement under different conditions.
For example, the dimeric structure of Al2Cl6 is retained in nonpolar solvents like benzene. This means that even when dissolved, the Al2Cl6 dimer does not break apart into AlCl3 monomers.
This retention is critical because it affects how the compound interacts with other substances and behaves in different environments.
The maintenance of the dimer structure in solutions like benzene highlights the stability and robustness of Al2Cl6 in various chemical contexts.

Bridging Bonds

Bridging bonds are special types of bonds where a single atom, usually a metal, is connected to two other atoms, creating a bridge-like structure.
In the case of the dimeric Al2Cl6, the compound contains such bridging bonds. Specifically, the dimer has two chlorine atoms that act as bridges between the two aluminum atoms.
These bridges are denoted as 3-center, 2-electron bonds, meaning that three atoms share two electrons to form the bond.
This bonding structure is unique and imparts specific properties to the dimer, such as its stability and reactivity. Understanding bridging bonds helps elucidate how complex molecules like Al2Cl6 are structured and how they behave chemically.