Rucete ✏ Chemistry In a Nutshell
1. VSEPR Theory (Valence-Shell Electron-Pair Repulsion)
- Electron pairs repel each other and arrange themselves as far apart as possible to minimize repulsion.
- Types of Electron Pair Repulsions (Strongest to Weakest):
- Lone pair – Lone pair > Lone pair – Bonding pair > Bonding pair – Bonding pair
2. Molecular Geometries Based on Electron Pairs
- The geometry of a molecule depends on the number of bonding pairs (B) and lone pairs (E) around the central atom (A).
| Electron Pairs | Molecular Geometry | Example | Bond Angle |
|---|
| AB₂ | Linear | BeCl₂, CO₂, HCN | 180° |
| AB₃ | Trigonal Planar | BF₃, SO₃, NO₃⁻ | 120° |
| AB₄ | Tetrahedral | CH₄, NH₄⁺, SiF₄ | 109.5° |
| AB₅ | Trigonal Bipyramidal | PCl₅ | 90°, 120° |
| AB₆ | Octahedral | SF₆, SeF₆ | 90° |
3. Molecular Geometries with Lone Pairs
- Lone pairs distort bond angles due to stronger repulsion than bonding pairs.
| Electron Pairs | Molecular Geometry | Example | Bond Angle |
|---|
| AB₃E | Trigonal Pyramidal | NH₃, PCl₃ | <109.5° |
| AB₂E₂ | Bent (Water Structure) | H₂O, OF₂ | 104.5° |
| AB₄E | Seesaw (Distorted Tetrahedron) | SF₄, XeO₂F₂ | <120°, <90° |
| AB₃E₂ | T-Shape | BrF₃, ICl₃ | <90° |
| AB₂E₃ | Linear | XeF₂, KrF₂ | 180° |
| AB₅E | Square Pyramidal | BrF₅, XeOF₄ | <90° |
| AB₄E₂ | Square Planar | XeF₄, ICl₄⁻ | 90° |
In a nutshell
- Lone pairs cause bond angles to shrink due to stronger repulsion.
- Linear molecules have 180° bond angles, while tetrahedral molecules have 109.5° bond angles.
- Trigonal bipyramidal and octahedral structures have a mix of 90° and 120° angles.
- More lone pairs = More distortion of bond angles.
"Lions Try To Teach Tigers, Only Silly People Bite!"
(Linear, Trigonal Planar, Tetrahedral, Trigonal Bipyramidal, Octahedral, Seesaw, Pyramidal, Bent)
