Question

The correct shape and I-I-I bond angles respectively in $I_3^-$ ion are :

• A. Linear; 180°
• B. Distorted trigonal planar; 135° and 90°
• C. T-shaped; 180° and 90°
• D. Trigonal planar; 120°

Hint:

For $sp^3d$ hybridization, lone pairs always prefer the equatorial positions where they have more space (120° angles) compared to axial positions (90°).

Answer 1

The Correct Option is A

Step 1: Central Iodine has 7 valence electrons + 1 from charge = 8. Two electrons form bonds with other I atoms, leaving 3 lone pairs.
Step 2: Steric number = 2 (bond pairs) + 3 (lone pairs) = 5. The hybridization is $sp^3d$.
Step 3: According to VSEPR theory, to minimize repulsion, the 3 lone pairs occupy equatorial positions, and the 2 bond pairs occupy axial positions.
Step 4: The geometry is trigonal bipyramidal, but the molecular shape is linear with a bond angle of 180°.