|Valence shell electron pair repulsion theory||Class 11|

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The Valence Shell Electron Pair Repulsion (VSEPR) Theory is a model used in chemistry to predict the geometry of individual molecules based on the number of electron pairs surrounding their central atoms. It was developed to explain molecular shapes and bond angles.
Key Principles of VSEPR Theory:
1. Electron Pair Repulsion: Electron pairs in the valence shell of an atom repel each other and arrange themselves as far apart as possible to minimize repulsion.
2. Types of Electron Pairs: Both bonding pairs (shared between atoms in bonds) and lone pairs (non-bonding electron pairs) contribute to the shape of the molecule. Lone pairs exert more repulsion than bonding pairs.
3. Electron Density Regions: The number of regions of electron density around the central atom determines the basic geometry of the molecule.
Molecular Geometries and Shapes:
Linear: Two regions of electron density, 180° bond angle (e.g., CO₂).
Trigonal Planar: Three regions of electron density, 120° bond angle (e.g., BF₃).
Tetrahedral: Four regions of electron density, 109.5° bond angle (e.g., CH₄).
Trigonal Bipyramidal: Five regions of electron density, bond angles of 90° and 120° (e.g., PCl₅).
Octahedral: Six regions of electron density, 90° bond angle (e.g., SF₆).
Effects of Lone Pairs:
Lone pairs reduce bond angles because they occupy more space than bonding pairs due to their stronger repulsion. For example:
NH₃ (Ammonia): Trigonal pyramidal shape due to one lone pair, bond angles are ~107°.
H₂O (Water): Bent shape due to two lone pairs, bond angles are ~104.5°.
The VSEPR theory is widely used to:
Predict molecular shapes.
Understand bond angles.
Explain the polarity and properties of molecules.
If you'd like examples or diagrams for specific molecules, let me know!
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