Chemical Bonding Lecture Notes

Previous Lectures Recap

• Part 1 Topics
  • Covalent bond formation
  • Octet rule and its limitations
  • Trick to write Lewis structures
• Part 2 Topics
  • Ionic bond formation
  • Lattice enthalpy and its role in stability of ionic compounds

Current Lecture Topics

• Focus on Fajans' Rule and Dipole Moment
  • Essential for competitive exams like NEET, JEE, CET

Ionic and Covalent Bonds Recap

• Ionic bonds formed by the transfer of electrons
  • Example: Formation of Na⁺ and Cl⁻ ions
• Covalent bonds formed by sharing electrons
  • Example: HCl molecule
• Key Point: Every ionic bond has some covalent character
  • Not 100% ionic
  • Covalent nature assessed through polarization

Polarization

• Determines covalent character in ionic bonds
• Definition: Distortion of electron cloud of anion by cation
• Factors affecting polarization:
  • Cation should be small, anion should be large
  • High charge on both cation and anion
  • Cations with pseudo-inert electronic configuration (e.g., Zn²⁺, Cu⁺)
• Fajans' Rule: Conditions for maximum polarization

Dipole Moment

• Determines ionic character in covalent bonds
• Definition: Product of charge and distance between atoms (bond length)
• Unit: Debye (D)
• Importance: More dipole moment indicates more ionic character

Examples and Comparison

• Covalent Character Comparison: CuCl vs NaCl
  • CuCl more covalent due to smaller cation size and pseudo-inert configuration
• Exercise Questions:
  • Compare KCl and AgCl for covalent character
  • Compare KCl and NaCl for ionic character

New Concepts

• Dipole in Molecules
  • Results from electronegativity differences
  • Positive and negative charges create a dipole
• Measurement of Dipole Strength
  • Dipole moment (µ) calculated as charge (Q) × distance (D)
  • Percentage ionic character = (Observed µ / Calculated µ) × 100

Vector Nature of Dipole Moment

• Dipole moments are vector quantities
• Examples:
  • CO₂: Linear structure, vectors cancel, dipole moment = 0
  • BF₃: Planar structure, vectors cancel, dipole moment = 0
  • Compare NH₃ and NF₃ dipole moments
    • NH₃ has a higher dipole moment due to vector alignment

Conclusion

• Further examples and bond parameters to be discussed in the next video
  • Importance of understanding molecular shape for predicting dipole moments

These notes summarize key points from the lecture on chemical bonding, focusing on the concepts of Fajans' rule and dipole moment, essential for understanding the nature of bonds in compounds. They include important definitions, examples, and exercises to practice the application of these concepts.