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

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.