Hybridisation
In the molecule BrF₃, the central bromine atom undergoes sp³d hybridisation. The molecular geometry of BrF₃ is:
Select the correct option:
Solution
T-shaped
- Count Valence Electrons: Br has 7 valence electrons and each F contributes 7, totalling 7+3×7=28 electrons.
- Assign Bonds and Lone Pairs on Br: Three Br–F bonds use 6 electrons. Each F gets 3 lone pairs (18 electrons total). Remaining on Br: 28−6−18=4 electrons = 2 lone pairs.
- Determine Electron-Pair Geometry: 3 bond pairs + 2 lone pairs = 5 electron domains → trigonal bipyramidal electron-pair arrangement (sp³d hybridisation).
- Position of Lone Pairs: Lone pairs preferentially occupy equatorial positions in a trigonal bipyramid to minimise 90° lp–bp repulsions. Both lone pairs sit in the equatorial plane.
- Resulting Shape: The three F atoms occupy the two axial positions and one equatorial position, giving a T-shaped molecular geometry with bond angles slightly less than 90° and ~180° between axial atoms.
- Why Not Others? Trigonal planar requires 0 lone pairs (e.g., BF₃). Trigonal pyramidal requires 1 lone pair with tetrahedral e-pair geometry (e.g., NH₃). Bent requires 2 lone pairs on tetrahedral arrangement (e.g., H₂O).
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About This Question
- Subject
- chemistry
- Chapter
- chemical bonding and molecular structure
- Topic
- hybridisation
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
T-shaped
- Count Valence Electrons: Br has 7 valence electrons and each F contributes 7, totalling 7+3×7=28 electrons.
- Assign Bonds and Lone Pairs on Br: Three Br–F bonds use 6 electrons. Each F gets 3 lone pairs (18 electrons total). Remaining on Br: 28−6−18=4 electrons = 2 lone pairs.
- Determine Electron-Pair Geometry: 3 bond pairs + 2 lone pairs = 5 electron domains → trigonal bipyramidal electron-pair arrangement (sp³d hybridisation).
- Position of Lone Pairs: Lone pairs preferentially occupy equatorial positions in a trigonal bipyramid to minimise 90° lp–bp repulsions. Both lone pairs sit in the equatorial plane.
- Resulting Shape: The three F atoms occupy the two axial positions and one equatorial position, giving a T-shaped molecular geometry with bond angles slightly less than 90° and ~180° between axial atoms.
- Why Not Others? Trigonal planar requires 0 lone pairs (e.g., BF₃). Trigonal pyramidal requires 1 lone pair with tetrahedral e-pair geometry (e.g., NH₃). Bent requires 2 lone pairs on tetrahedral arrangement (e.g., H₂O).
This medium difficulty chemistry question is from the chapter chemical bonding and molecular structure, covering the topic of hybridisation. It appeared in the 2025 exam.
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