What NEET Asks
- Predicting molecular shapes using VSEPR theory and hybridization is a frequent question type in NEET.
- Questions often involve comparing bond angles or identifying the correct geometry for various species.
- Expect 1-2 questions from Chemical Bonding, frequently including molecular geometry concepts.
Key Points
- VSEPR Theory: Explains molecular shapes based on minimizing repulsion between electron pairs (lone pairs and bond pairs) around the central atom.
- Repulsion order: Lone pair-lone pair (LP-LP) > Lone pair-bond pair (LP-BP) > Bond pair-bond pair (BP-BP).
- Hybridization: Mixing of atomic orbitals to form new hybrid orbitals; determines electron domain geometry.
- Electron Geometry (arrangement of all electron domains) differs from Molecular Geometry (arrangement of atoms) if lone pairs are present.
- Common geometries include Linear (sp), Trigonal planar (sp2), Tetrahedral (sp3), Trigonal bipyramidal (sp3d), and Octahedral (sp3d2).
Must-Know Formula / Reaction
- Steric Number (SN) = (Number of σ bonds) + (Number of lone pairs on central atom)
- SN 2 → sp hybridization → Linear electron geometry
- SN 3 → sp2 hybridization → Trigonal planar electron geometry
- SN 4 → sp3 hybridization → Tetrahedral electron geometry
- SN 5 → sp3d hybridization → Trigonal bipyramidal electron geometry
- SN 6 → sp3d2 hybridization → Octahedral electron geometry
- Note: Only sigma (σ) bonds contribute to steric number, not pi (π) bonds.
Common Mistakes
- Students often confuse electron geometry with molecular geometry, especially when lone pairs modify the shape.
- Don't forget to correctly count lone pairs on the central atom while calculating the steric number.
- Incorrectly assuming bond angles are always ideal (e.g., 109.5° for sp3) without considering lone pair repulsion.
Rapid Revision
Mastering VSEPR and Hybridization is key for predicting molecular shapes. Remember that lone pairs exert greater repulsion, causing deviations from ideal bond angles. Quickly calculate the steric number (σ bonds + lone pairs) to determine hybridization and electron geometry, then derive the molecular geometry.