Molecular Geometry and VSEPR Model
Introduction
- Importance of understanding molecule arrangement in 3D space
- Influence of geometry on molecular chemistry
VSEPR Model
- Stands for Valence Shell Electron Pair Repulsion
- Predicts molecular shape based on electron repulsion
Key Concepts
- Electron Clouds: Negatively charged, repel each other
- Lowest Energy State: Molecules adjust to minimize energy, keeping atoms far apart
Examples of Molecular Geometry
-
Carbon Dioxide (CO2):
- Carbon has two electron domains
- Hybridization: sp (1 s + 1 p orbital)
- Geometry: Linear (180-degree bond angles)
-
Boron Trifluoride (BF3):
- Boron has three electron domains
- Hybridization: sp2 (1 s + 2 p orbitals)
- Geometry: Trigonal Planar (120-degree bond angles)
-
Methane (CH4):
- Carbon has four electron domains
- Hybridization: sp3 (1 s + 3 p orbitals)
- Geometry: Tetrahedral (109.5-degree bond angles)
-
Trigonal Bipyramidal Geometry:
- 5 electron domains
- Hybridization: sp3d
- Geometry: Trigonal Bipyramidal (90 and 120-degree bond angles)
-
Octahedral Geometry:
- 6 electron domains
- Hybridization: sp3d2
- Geometry: Octahedral (90-degree bond angles)
Electron Domains
- Counting Electron Domains: Determines hybridization and geometry
- Types of Electron Domains: Covalent bonds and lone pairs
Examples of Molecular Geometry with Lone Pairs
-
Ammonia (NH3):
- Nitrogen has three bonds and one lone pair
- Hybridization: sp3
- Geometry: Trigonal Pyramidal
-
Water (H2O):
- Oxygen has two bonds and two lone pairs
- Hybridization: sp3
- Geometry: Bent
Summary
- Electron domains (covalent bonds or lone pairs) determine the central atom's hybridization
- Hybridization indicates electron domain geometry
- Molecular geometry varies based on lone pairs vs. bonds
Study Tips
- Always start with a correct Lewis dot structure
- Count electron domains to determine geometry
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