Chapter 3 Simple Bonding Theory
Post on 20-Jan-2016
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Chapter 3Simple Bonding Theory
• Lewis Dot Structures–Resonance–Formal Charge
• VSEPR: the subtle effects
Lewis Dot Structures
1. Count valence electrons2. Arrange atoms3. Add bonds4. Add lone pairs5. Convert lone pairs to bonding pairs (octet rule and exceptions)
Lewis Dot Structures
• Examples:CO2
SO3
N2OXeF4
ClF3
PCl6–
Why does the octet rule work?
More complex
NO2
NO
Formal Charge
= Group # - #unshared electrons on atom - # bonds to atom
Example: O3
Resonance
Example: SO3
Resonance and Formal Charge
Example: SCN-
Resonance and Formal Charge
Example: SCN-
Octet Rule vs. Pi Bonding Trends
BeF2 and
BF3
Octet Rule vs. Formal Charge
• Always follow octet ruleExceptions? SO4
2-
VSEPR
•Maximize “personal space”• CO2, SO3, SO4
2–, PCl5, SF6
• 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
Pi Bonds vs. Lone Pairs
Which take up more room: lone pairs or a pi bond?
Electronegativity Effects
Molecule X-P-X Angle o
PF3 97.8
PCl3 100.3
PBr3 101
Explain this trend.
Electronegativity Effects
Molecule H-X-H Angle o H2O 104.4H2S 92.1H2Se 90.6
Explain this trend.
Molecule X-As-X Angle o AsF3 AsCl3 AsBr3
Predict this trend.
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