CHM227 - Review Exam #1

CHM227 - Review Exam #1 - Bond Strengths and Lengths 1....

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Bond Strengths and Lengths 1. Shorter bonds are stronger. 2. Bonds between H and C, N, and O are strong. 3. Bonds between C and N or O are strong. 4. C-X bonds are weaker and longer moving down the column. 5. Double and triple bonds are shorter and stronger. Bond Bond Dissociation Energy C – H 98 kcal/mol 410 kJ/mol N – H 92 kcal/mol 385 kJ/mol O – H 109 kcal/mol 456 kJ/mol C – C 81 kcal/mol 339 kJ/mol C – N 66 kcal/mol 276 kJ/mol C – O 79 kcal/mol 330 kJ/mol C – F 116 kcal/mol 485 kJ/mol C – Cl 79 kcal/mol 330 kJ/mol C – Br 66 kcal/mol 276 kJ/mol C – I 52 kcal/mol 217 kJ/mol C = C 145 kcal/mol 606 kJ/mol C ≡ C 198 kcal/mol 828 kJ/mol C = O 173 kcal/mol 723 kJ/mol C ≡ N 204 kcal/mol 854 kJ/mol Formal Charge = (Valence Electrons) – (Unshared electrons) – ½(Shared Electrons) Bond Bond Length C – H 1.10 N – H 1.00 O – H 1.00 C – C 1.54 C – N 1.47 C – O 1.41 C – F 1.38 C – Cl 1.78 C – Br 1.94 C – I 2.14 C = C 1.34 C ≡ C 1.20 C = O 1.20 C ≡ N 1.16
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Degree of Unsaturation (DU) = [(2n + 2) – x] /2 Ion-Ion Interaction – these are the strongest because they involve the most charge. Ion-Dipole Interaction – involves an attraction between a charged ion and a polar molecule Dipole-Dipole Interaction – exists between neutral polar molecules. The partially negative end attracts the partially positive end. They need to be close together to form strong interactions. Dipole-Induced Dipole Interaction – this is the force attracting a polar molecule to a non-polar molecule. Instantaneous Dipole-Induced Dipole Interaction (London Forces) – The attraction between non-polar molecules. Van der Waals Forces
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CHM227 - Review Exam #1 - Bond Strengths and Lengths 1....

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