Question

The bond angles \( b_1, b_2, b_3 \) in the above structure are respectively in \( ^\circ \):

• A. \( 79, 101, 118 \)
• B. \( 118, 101, 79 \)
• C. \( 79, 118, 101 \)
• D. \( 118, 79, 101 \)

Hint:

In dimeric \( Al_2Cl_6 \), the presence of bridging chlorine atoms reduces bond angles due to steric hindrance. The terminal Cl-Al-Cl bond has the largest bond angle (~118°), while the bridging Al-Cl-Al bond has the smallest (~79°).

Answer 1

The Correct Option is D

To determine the bond angles b₁, b₂, b₃, we need to analyze the structure shown in the accompanying image. Bond angles are influenced by the hybridization and spatial arrangement of atoms in molecules.

1. Determine the electronic geometry and hybridization:
In molecules, bond angles depend on the hybridization state of the central atom. The typical angles are:

• sp³ hybridization → approximately 109.5°
• sp² hybridization → approximately 120°
• sp hybridization → 180°

 2. Identify and match angles with options:
Given that the correct set of angles is 118°, 79°, 101°, and assuming the molecular structure contains distortions from ideal geometries:

• An angle of 118° could correspond to a slightly distorted sp² geometry.
• The small angle 79° may result from steric strain or a ring structure imposing sharp bond angles.
• The intermediate angle 101° may arise from a distorted tetrahedral or irregular trigonal geometry.

3. Conclusion:
Based on molecular geometry considerations and the provided data, the correct bond angle assignments are: 
b₁ = 118°, b₂ = 79°, b₃ = 101°, indicating deviations from ideal hybridized geometries due to structural distortions.

Answer 2

In the given structure, which is \(Al_2Cl_6\), each aluminum atom is surrounded by four chlorine atoms in a tetrahedral arrangement. However, the two aluminum atoms are bonded together through two bridging chlorine atoms.

\(b_1\) represents the Cl-Al-Cl bond angle within the four-membered ring (formed by the two aluminum and two bridging chlorine atoms). Due to ring strain, this angle is smaller than the ideal tetrahedral angle of 109.5°.

\(b_2\) is the Al-Cl-Al angle formed by the bridging chlorines. This angle is larger than the ideal tetrahedral angle.

\(b_3\) represents the Cl-Al-Cl bond angle involving the terminal chlorine atoms (not part of the bridge). This angle is close to the ideal tetrahedral angle.

Therefore, \(b_1 < b_3 < b_2\), and the correct values are approximately \(b_1 = 79^\circ\), \(b_2 = 101^\circ\), and \(b_3 = 118^\circ\). 
So the order is 118, 79, 101.