Lecture Notes on Bond Length and Bond Strength

Comparing HF and HBr

Bond Length:
- HBr has a longer bond length compared to HF.
- HF bond length: ~0.92 angstroms
- HBr bond length: ~1.4 angstroms
Atomic Size:
- Bromine is larger than fluorine, resulting in a longer bond with hydrogen.
- As you go down the halogen group (Fluorine to Iodine), atomic size increases.
Bond Strength:
- HF has a stronger bond due to shorter bond length.
- HF bond strength: ~571 kJ/mol
- HBr bond strength: ~366 kJ/mol
Inverse Relationship:
- As bond length increases, bond strength decreases.

Trend:
- Bond length increases and bond strength decreases as you move from fluorine to iodine.
Examples:
- HF: 0.92 angstroms, 570 kJ/mol
- HBr: 1.4 angstroms, 366 kJ/mol
- HI (Iodine): 1.6 angstroms, 298 kJ/mol

Carbon-Bromine vs. Carbon-Iodine:
- CI bond is longer and weaker than CBr bond due to iodine's larger size.

Types & Strengths:
- Single bonds > Double bonds > Triple bonds in length
- Triple bonds > Double bonds > Single bonds in strength
Examples:
- Ethane C-C: 1.5 angstroms, weakest
- Ethene C=C: 1.3 angstroms, moderate strength
- Ethyne (acetylene) C≡C: 1.2 angstroms, strongest

Bond Length:
- Ethane CH: ~1.1 angstroms
- Ethene CH: ~1.08 angstroms
- Ethyne CH: ~1.06 angstroms
Bond Strength:
- Ethane CH: ~423 kJ/mol
- Ethene CH: ~460 kJ/mol
- Ethyne CH: ~560 kJ/mol
Hybridization Impact:
- Ethane (sp3): More p-character, longer bond.
- Ethene (sp2): Moderate s-character, moderate length.
- Ethyne (sp): More s-character, shortest bond.

S Character Influence:
- Greater s-character results in shorter bonds.
- Sp > Sp2 > Sp3 in terms of s-character.
Techniques for Determining Bond Lengths:
- Look at adjacent bonds or hybridization status of bonded carbons.
- Bonds surrounded by longer bonds are longer due to higher p-character.