Chemistry Lecture: Determining Intermolecular Forces

Introduction to Intermolecular Forces (IMF)

• Intermolecular Force (IMF): Attraction between molecules, e.g., attraction between water molecules.
• Intramolecular Forces (Bonds): Attraction within molecules, such as covalent bonds (e.g., O-H bonds).

Types of Intermolecular Forces

1. London Dispersion Forces (LDF): Present in all molecules, especially nonpolar molecules.
2. Dipole-Dipole Forces: Occur in polar molecules in addition to LDF.
3. Hydrogen Bonding: Occurs if H is directly attached to F, O, or N; includes LDF and dipole-dipole.

Determining Intermolecular Forces in Compounds

• Nonpolar Compounds: Only have London dispersion forces.
• Polar Compounds: Have London dispersion forces and dipole-dipole forces.
• Compounds with H-F, H-O, or H-N: Have London dispersion forces, dipole-dipole forces, and hydrogen bonding.

Example Problems and Solutions

• Carbon Dioxide (CO₂):
  • Draw the Lewis structure: O=C=O.
  • It's nonpolar (central atom, C, has no lone pairs, and surrounding atoms O are the same).
  • IMF: London dispersion forces only.
• Sulfur Tetrafluoride (SF₄):
  • Lewis structure indicates the central atom, S, has a lone pair.
  • Polar molecule: Has London dispersion and dipole-dipole forces (no hydrogen bonding as no H-F, H-O, or H-N).
• Methylamine (CH₃NH₂):
  • Contains N-H bond directly, suggesting hydrogen bonding.
  • IMF: London dispersion, dipole-dipole, and hydrogen bonding.
• Pentane (C₅H₁₂):
  • Contains only C and H, thus nonpolar.
  • IMF: London dispersion forces only.
• Neon (Ne):
  • Single element atom, nonpolar.
  • IMF: London dispersion forces only.
• Hydrogen Chloride (HCl):
  • Polar due to Cl being more electronegative than H.
  • IMF: London dispersion and dipole-dipole forces (no hydrogen bonding).

Steps to Determine IMF in a Compound

1. Draw the Lewis Structure.
2. Determine Polarity: Use a checklist to see if it's polar or nonpolar.
3. Identify Bonds: Look for direct H-F, H-O, or H-N bonds for hydrogen bonding.

Additional Resources

• For detailed tutorials on drawing Lewis structures and determining polarity, visit the speaker's website.
• Website: conquerchemistry.com for a guide on acing chemistry.

Conclusion

• Focus on understanding the main types of IMFs and their conditions.
• Practice with example problems to solidify understanding.
• Use additional resources for comprehensive learning.