1. CHE-240 Unit 1 Structure and Stereochemistry of Alkanes CHAPTER ONE
Terrence P. Sherlock
Burlington County College
2004

2. Bond Formation Ionic bonding: electrons are transferred.
Covalent bonding: electron pair is shared.
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3. Satisfy the octet rule! =>
Lewis Structures
Bonding electrons
Nonbonding electrons or lone pairs
Satisfy the octet rule! =>
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4. Multiple Bonding
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5. Dipole Moment Amount of electrical charge x bond length.
Charge separation shown by electrostatic potential map (EPM).
Red indicates a partially negative region and blue indicates a partially positive region.
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6. Electronegativity and Bond Polarity
Greater EN means greater polarity
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7. Calculating Formal Charge
For each atom in a valid Lewis structure:
Count the number of valence electrons
Subtract all its nonbonding electrons
Subtract half of its bonding electrons
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8. Ionic Structures X
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9. Resonance
Only electrons can be moved (usually lone pairs or pi electrons).
Nuclei positions and bond angles remain the same.
The number of unpaired electrons remains the same.
Resonance causes a delocalization of electrical charge.
Example=>
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10. Resonance Example The real structure is a resonance hybrid.
All the bond lengths are the same.
Each oxygen has a -1/3 electrical charge =>
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11. Major Resonance Form has as many octets as possible.
has as many bonds as possible.
has the negative charge on the most electronegative atom.
has as little charge separation as possible.
Example=>
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12. Major Contributor? major minor, carbon does not have octet. =>
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13. Chemical Formulas CH3COOH C2H4O2 CH2O =>
Full structural formula (no lone pairs shown)
Line-angle formula
Condensed structural formula
Molecular formula
Empirical formula
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14. Arrhenius Acids and Bases
Acids dissociate in water to give H3O+ ions.
Bases dissociate in water to give OH- ions.
Kw = [H3O+ ][OH- ] = 1.0 x at 24°C
pH = -log [H3O+ ]
Strong acids and bases are 100% dissociated.
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15. BrØnsted-Lowry Acids and Bases
Acids can donate a proton.
Bases can accept a proton.
Conjugate acid-base pairs.
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acid
base
conjugate
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16. Acid and Base Strength Acid dissociation constant, Ka
Base dissociation constant, Kb
For conjugate pairs, (Ka)(Kb) = Kw
Spontaneous acid-base reactions proceed from stronger to weaker.
pKa 4.74
pKb 3.36
pKb 9.26
pKa 10.64
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17. Determining Relative Acidity
Electronegativity
Size
Resonance stabilization of conjugate base =>
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18. Electronegativity
As the bond to H becomes more polarized, H becomes more positive and the bond is easier to break.
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19. Size
As size increases, the H is more loosely held and the bond is easier to break.
A larger size also stabilizes the anion.
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20. Resonance
Delocalization of the negative charge on the conjugate base will stabilize the anion, so the substance is a stronger acid.
More resonance structures usually mean greater stabilization.
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21. Lewis Acids and Bases Acids accept electron pairs = electrophile
Bases donate electron pairs = nucleophile
nucleophile
electrophile
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22. POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5TH EDITION” L. G
POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5TH EDITION” L.G. WADE ALL MATERIALS USED WITH PERMISSION OF AUTHOR PRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGE ORGANIC CHEMISTRY COURSE BY: ANNALICIA POEHLER STEFANIE LAYMAN CALY MARTIN
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