Molecular Geometry and Electron Domains
Summary of Molecular Geometry
Overview of Electron Domains
- Electron domains are regions around a central atom where electrons are likely to be found. Each domain can be a:
- Lone pair
- Single bond
- Double bond
- Triple bond
- Single electron
Molecular Geometry Based on Number of Electron Domains
2 Electron Domains
- Electron Geometry: Linear
- Molecular Geometry: Linear
- Bond Angle: 180°
- Examples:
- CO2 (2 bonding domains)
- Polar or nonpolar? Nonpolar
3 Electron Domains
- Electron Geometry: Trigonal Planar
- Molecular Geometry:
- Trigonal Planar for 3 bonding domains
- Bent for 2 bonding domains and 1 lone pair
- Bond Angles: 120° (Trigonal Planar); <120° (Bent)
- Examples:
- BF3 (Trigonal Planar)
- SO2 (Bent, polar)
4 Electron Domains
- Electron Geometry: Tetrahedral
- Molecular Geometry:
- Tetrahedral for 4 bonding domains
- Trigonal Pyramidal for 3 bonding domains and 1 lone pair
- Bent for 2 bonding domains and 2 lone pairs
- Bond Angles: 109.5° (Tetrahedral); <109.5° (Trigonal Pyramidal, Bent)
- Examples:
- CH4 (Tetrahedral)
- NH3 (Trigonal Pyramidal)
- H2O (Bent, polar)
5 Electron Domains
- Electron Geometry: Trigonal Bipyramidal
- Molecular Geometry:
- Trigonal Bipyramidal for 5 bonding domains
- Seesaw for 4 bonding domains and 1 lone pair
- T-shaped for 3 bonding domains and 2 lone pairs
- Linear for 2 bonding domains and 3 lone pairs
- Bond Angles: 120° (equatorial); 90° (axial)
- Examples:
- PCl5 (Trigonal Bipyramidal)
- SF4 (Seesaw)
- ClF3 (T-shaped)
- XeF2 (Linear, nonpolar)
6 Electron Domains
- Electron Geometry: Octahedral
- Molecular Geometry:
- Octahedral for 6 bonding domains
- Square Pyramidal for 5 bonding domains and 1 lone pair
- Square Planar for 4 bonding domains and 2 lone pairs
- Bond Angles: 90°
- Examples:
- SF6 (Octahedral)
- BrF5 (Square Pyramidal)
- XeF4 (Square Planar)
Recap of Bonding and Nonbonding Domains
- Bonding Domains: Electrons that are shared between atoms that form bonds.
- Nonbonding Domains: Electrons that are not shared, existing as lone pairs around the central atom, influencing shape and bond angles.
Summary Table of Molecular Geometries
| Electron Groups | Bonding Groups | Lone Pairs | Electron Geometry | Molecular Geometry | Approximate Bond Angles |
|---|
| 2 | 2 | 0 | Linear | Linear | 180° |
| 3 | 3 | 0 | Trigonal Planar | Trigonal Planar | 120° |
| 2 | 1 | Trigonal Planar | Bent | <120° |
| 4 | 4 | 0 | Tetrahedral | Tetrahedral | 109.5° |
| 3 | 1 | Tetrahedral | Trigonal Pyramidal | <109.5° |
| 2 | 2 | Tetrahedral | Bent | <109.5° |
| 5 | 5 | 0 | Trigonal Bipyramidal | Trigonal Bipyramidal | 120° (equatorial) / 90° (axial) |
| 4 | 1 | Trigonal Bipyramidal | Seesaw | <120° (equatorial) / <90° (axial) |
| 3 | 2 | Trigonal Bipyramidal | T-shaped | <90° |
| 2 | 3 | Trigonal Bipyramidal | Linear | 180° |
| 6 | 6 | 0 | Octahedral | Octahedral | 90° |
| 5 | 1 | Octahedral | Square Pyramidal | <90° |
| 4 | 2 | Octahedral | Square Planar | 90° |