Chapter 3 Simple Bonding Theory Lewis Dot Structures
Chapter 3 Simple Bonding Theory • Lewis Dot Structures – Resonance – Formal Charge • VSEPR: the subtle effects
Lewis Dot Structures 1. Count valence electrons 2. Arrange atoms 3. Add bonds 4. Add lone pairs 5. Convert lone pairs to bonding pairs (octet rule and exceptions)
Lewis Dot Structures • Examples: CO 2 SO 3 N 2 O Xe. F 4 Cl. F 3 – PCl 6
Why does the octet rule work?
More complex NO 2 NO
Formal Charge = Group # - #unshared electrons on atom - # bonds to atom Example: O 3
Resonance Example: SO 3
Resonance and Formal Charge Example: SCN-
Resonance and Formal Charge Example: SCN-
Octet Rule vs. Pi Bonding Trends Be. F 2 and BF 3
Octet Rule vs. Formal Charge • Always follow octet rule Exceptions? SO 42 -
VSEPR • Maximize “personal space” • CO 2, SO 3, SO 42–, PCl 5, SF 6 • Lone pairs vs. bonding pairs? • Single bonds vs. multiple bonds? • Electronegativity effects
VSEPR
Lone Pair Effects
Pi Bonds vs. Lone Pairs: Guess these bond angles.
Pi Bonds vs. Lone Pairs: Guess these bond angles.
Pi Bonds vs. Lone Pairs
Pi Bonds vs. Lone Pairs Which take up more room: lone pairs or a pi bond?
Electronegativity Effects
Electronegativity Effects Molecule X-P-X Angle o PF 3 97. 8 PCl 3 100. 3 PBr 3 101 Explain this trend.
Electronegativity Effects Molecule X-P-X Angle o PF 3 97. 8 PCl 3 100. 3 PBr 3 101 Terminal Atom Effects: F: Electron density of the bond pairs is mostly near the F. Electron density near the central atom is less, which decreases bond pair – bond pair repulsion near the P.
Electronegativity Effects Molecule H 2 O H 2 S H 2 Se H-X-H Angle o 104. 4 92. 1 90. 6 Explain this trend.
Electronegativity Effects Molecule H 2 O H 2 S H 2 Se H-X-H Angle o 104. 4 92. 1 90. 6 Explain this trend. Central atom effects: O: as O pulls more electron density toward it, bonds have more electron density near the central atom. This causes greater bond pair – bond pair repulsions.
Electronegativity Effects Molecule As. F 3 As. Cl 3 As. Br 3 X-As-X Angle o Predict this trend.
Predicting Positions of Different Atoms PF 3 Cl 2 Are Cl atoms axial or equatorial?
Homework Chapter 3 7, 9 acde, 11, 12, 14, 29, 30 a
- Slides: 29