Important Dates
- HW and modules deadlines:
- Lecture 24 HW due: November 7th, 2025, 11:59 PM
- Lecture 25 HW due: November 10th, 2025, 11:59 PM
- ALEKS Chapter 8 Module due: November 9th, 2025, 11:59 PM
- Exam 4 on: November 19th, 2025
Valence-Shell Electron-Pair Repulsion (VSEPR) Theory
- Electron groups determine electron-domain geometry:
- 2: Linear
- 3: Trigonal planar
- 4: Tetrahedral
- 5: Trigonal bipyramidal
- 6: Octahedral
- Molecular shape influenced by bonded atoms vs lone pairs.
Electron Group Geometry and Molecular Geometry Summary
| # of Electron Groups | # of Bonded Atoms | # Lone Pairs | AXmEn | Electron-Domain Geometry | Molecular Geometry | Predicted Bond Angle |
|---|---|---|---|---|---|---|
| 2 | 2 | 0 | AX2 | Linear | Linear | 180° |
| 3 | 3 | 0 | AX3 | Trigonal Planar | Trigonal Planar | 120° |
| 3 | 2 | 1 | AX2E | Trigonal Planar | Bent | <120° |
| 4 | 4 | 0 | AX4 | Tetrahedral | Tetrahedral | 109.5° |
| 4 | 3 | 1 | AX3E | Tetrahedral | Trigonal pyramidal | <109.5° |
| 5 | 5 | 0 | AX5 | Trigonal Bipyramidal | Trigonal Bipyramidal | 90°/120° |
| 6 | 6 | 0 | AX6 | Octahedral | Octahedral | 90° |
Molecular Polarity
- Determined by electronegativity difference (ΔEN):
- Polar bond if ΔEN > 0.4
- Non-polar bond if ΔEN < 0.4
- Asymmetry in molecular shape leads to polar molecules.
Covalent Bonding & Valence Bond Theory
- Covalent bonds form through orbital overlap configurations:
- Orbitals share electrons; max of two electrons (paired spins).
- Exothermic nature: Bonds lower potential energy.
Hybridization
- Atomic orbitals mix to form hybrid orbitals; shapes depend on geometry:
- sp (linear), sp² (trigonal planar), sp³ (tetrahedral).
- Hybridization is necessary for individual bond structures.
Sigma and Pi Bonds
- Sigma (σ) bonds: Formed through head-on overlap; cylindrical symmetry.
- Pi (π) bonds: Formed side-on; weaker than σ bonds, restrict rotation.
- Bond Order:
- Single bond: BO = 1
- Double bond: BO = 2 (1 σ + 1 π)
- Triple bond: BO = 3 (1 σ + 2 π)
Practice Concepts
- Calculate hybridization, molecular geometry, bond angles for given compounds (e.g., SF4, BF3).
- Analyze bonding structure and formal charges in Lewis structures.