Question

In a molecule central atom 'A' has sp³d- hybridisation and surrounded by some s-bond pairs and some lone pairs. In this molecule 3 structures are possible. In each structure electron pair repulsion at 90° are given below Structure-1: Lone pair | lone pair = 0; lone pair | bond pair = 6; bond pair | bond pair = 0 Structure-2: Lone pair | lone pair = 1; lone pair | bond pair = 3; bond pair | bond pair = 2 Structure-3: Lone pair | lone pair = 0; lone pair | bond pair = 4; bond pair | bond pair = 2 Molecule has maximum stability when it has

• A. Structure-1
• B. Structure-2
• C. Structure-3
• D. both Structure-2 and Structure-3

Answer 1

Answer: (A)

Structure-1

Answer 2

The sp³d hybridization leads to a trigonal bipyramidal electron geometry. Stability is determined by minimizing electron pair repulsions, especially at 90°. Lone pairs cause greater repulsion than bond pairs, and lone pair-lone pair repulsions are strongest.

• Structure-1: 0 LP-LP@90°, 6 LP-BP@90°, 0 BP-BP@90°. This configuration (likely 3 lone pairs, 2 bond pairs with lone pairs in equatorial positions) minimizes repulsions effectively.
• Structure-2: 1 LP-LP@90°, 3 LP-BP@90°, 2 BP-BP@90°. The presence of a lone pair-lone pair repulsion at 90° makes this structure less stable.
• Structure-3: 0 LP-LP@90°, 4 LP-BP@90°, 2 BP-BP@90°. While it avoids LP-LP@90°, it has more LP-BP@90° interactions than Structure-1.

Structure-1 represents the most stable arrangement due to the absence of LP-LP repulsions at 90° and the optimal placement of lone pairs in equatorial positions, minimizing overall repulsion.