section 8.3 bond properties
DESCRIPTION
Section 8.3 Bond Properties. In this section… Bond order Bond length Bond energy Bond energy and H. Bond Properties. Bond Order = # bonds between two atoms. Bond Length = distance between nuclei of bonded atoms. Bond Length Trends: Larger atoms make longer bonds. - PowerPoint PPT PresentationTRANSCRIPT
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Section 8.3Bond Properties
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Bond Properties
In this section…
a. Bond orderb. Bond lengthc. Bond energyd. Bond energy and H
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Bond Order = # bonds between two atoms
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Bond Length = distance between nuclei of bonded atoms
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Bond Length Trends: Larger atoms make longer bonds
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Bond Length Trends: Multiple bonds are shorter than single bonds
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Bond Energy: Energy required to break one mole of bonds
O-H bond energy = 463 kJ/mol
Bond energies range from about 150 kJ/mol to about 950 kJ/mol
Single bonds are from 150 – 500 kJ/mol
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Bond Energy Trends: Larger atoms make weaker bonds
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Bond Energy Trends: Multiple bonds are stronger than single bonds
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Resonance Effects on Bond Properties
number of bonding pairsBond order = number of bond locations
Bond length and energy follow same trends:
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Using Bond Energy to Calculate Enthalpy Change
Breaking bonds requires energy: endothermic
Forming bonds releases energy: exothermic
rxnH = energy of bond broken energy of bonds formed
NOTE: This only works for gas-phase reactions.
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Using Bond Energy to Calculate Enthalpy Change
rxnH = energy of bond broken energy of bonds formed
Bond Energies, kJ/molH-H 436N-H 391N≡N 945
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Section 8.4Charge Distribution in Molecules
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Bond Properties
In this section…
a. Electronegativity and Bond polarityb. Formal chargec. Resonance structuresd. Partial charge
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Bond Polarity
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Electronegativity
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Continuum from Covalent to Ionic Bonding: Bond Character
The larger the electronegativitydifference, the more polar thebond.
More polar = more ionic character.Less polar = more covalent character.
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Electron Distribution in Molecules
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Formal Charge: Assume all bonding electrons shared evenly between bonded atoms
Formal Charge = Group # - # lone pair electrons – ½ # bonding electrons
Formal Charge = Group # - # assigned electrons
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Using Formal Charge to Rank Nonequivalent Resonance Structures
Rule 1: avoid large or split chargesRule 2: negative charges are more stable on more electronegative atoms
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Electron Distribution in Molecules: Partial Charges
Actual atoms in molecules have partial charges.
Oxidation Number -2 +4 -2 -2 +4 -3Formal Charge 0 0 0 -1 0 0