Question

Geometry of a molecule \( \text{AB}_3\text{E}_2 \) with 3 bond pairs and 2 lone pairs

Hint:

In a trigonal bipyramidal electron geometry (\( sp^3d \)), lone pairs always occupy equatorial positions first because the bond angles are \( 120^\circ \), which provides more space and minimizes repulsion compared to axial positions (\( 90^\circ \)).

Answer 1

Step 1: Understanding the Concept:
According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, the geometry of a molecule depends on the total number of electron domains around the central atom.
Step 2: Key Formula or Approach:
The approach uses VSEPR rules where Steric Number = (Number of Bond Pairs) + (Number of Lone Pairs). Minimizing lone-pair repulsions defines the final molecular shape.
Step 3: Detailed Explanation:
The molecule has the generic formula \( \text{AB}_3\text{E}_2 \).
It possesses 3 bond pairs (B) and 2 lone pairs (E), making a total of 5 electron domains.
With 5 electron domains, the central atom undergoes \( sp^3d \) hybridization.
The basic electron domain geometry for 5 domains is trigonal bipyramidal.
To minimize repulsion (especially lone pair-lone pair and lone pair-bond pair repulsions), the lone pairs occupy the more spacious equatorial positions.
The three bond pairs occupy the remaining two axial positions and one equatorial position.
The resulting molecular geometry, observing only the atoms and ignoring the lone pairs visually, takes the shape of the letter 'T'.
Therefore, the molecular geometry is T-shaped.
Step 4: Final Answer:
The molecular geometry is T-shaped.