ch1 a
TRANSCRIPT
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Bonding Types – ionic and covalent
Covalent Bonding – equal/unequal sharing
Bonding Model – Lewis Structures (with formal charge and resonance structures)
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How compounds are held together: covalent vs ionic bonding
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Electronegativity:measure of attraction for electrons in a bond
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0 0.4 1.9
Nonpolar
Very slightly polar(called nonpolar)
Polar
No sharing(Ionic bond)
Electronegativity Difference
DEN and Bond Polarity Scale
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Electronegativity Trends
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Bond vs Molecular Polarity
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Lewis Structures: model to describe bonding in covalent molecules
- Valence electrons represented by dots- Bonding pair represented by line- Valence e- so 2 for H and 8 for 2nd row elements
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Formal Charge: way of keeping track* of where charge is within a molecule
FC = group number – nonbonding e- – ½ shared e-
Electrons that contribute to atom’s charge:1. All of unshared electrons2. Half of shared electrons
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Resonance (when 1 Lewis structure doesn’t tell the story well)
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Resonance “rules of thumb”
• Must be valid Lewis structure• Move electrons, not nuclei• Number of unpaired electrons (if any) remain
the same• Major contributor has lowest energy (see
other rules)• Resonance – most important when charge is
delocalized
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Comparing Resonance Structures
• As many octets as possible• As many bonds as possible• Any negative charges on electronegative
atoms• As little charge separation as possible
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Common Bonding Patterns