Intermolecular Forces in Molecules

Overview

• Identify and list all possible intermolecular forces in a molecule.
• Determine the strongest intermolecular force present.
• Intermolecular forces are not mutually exclusive; a molecule can have multiple forces simultaneously.
• Examples of intermolecular forces include:
  • Ion-ion interactions (strongest)
  • Hydrogen bonds
  • Dipole-dipole interactions
  • Dispersion forces (weakest)

Key Points

• Dispersion Forces: Present in all molecules due to electron fluctuations causing temporary imbalances.
• Hydrogen Bonds: A subset of dipole-dipole interactions; if a molecule has a hydrogen bond, it also has a dipole-dipole interaction.
• Dipole-Dipole Interactions: Occur in molecules with polar bonds but not necessarily hydrogen bonds.
• Ion-Ion Interactions: Present in ionic compounds; not applicable to non-ionic molecules like water.

Examples of Intermolecular Forces

Water (H₂O)

• Dispersion Forces: Always present.
• Hydrogen Bonds: Between oxygen and hydrogen atoms.
• Dipole-Dipole Interactions: Due to polar nature of water molecules.
• Ionic Interaction: Not present as water is non-ionic.

Alkene

• Dispersion Forces: Always present.
• Dipole-Dipole Interactions: Not present as alkenes are non-polar.
• Hydrogen Bonds: Absent due to non-polarity.
• Ionic Interaction: Not applicable.
• Physical Properties: Likely gaseous or liquid with low boiling point.

2-Chlorobutane

• Dispersion Forces: Always present.
• Dipole-Dipole Interactions: Present due to polar nature of the chlorine atom.
• Hydrogen Bonds: Not present; chlorine is not part of FON (Fluorine, Oxygen, Nitrogen).

Ammonia (NH₃)

• Dispersion Forces: Always present.
• Dipole-Dipole Interactions: Present due to lone pair imbalance.
• Hydrogen Bonds: Present between nitrogen and hydrogen.
• Ionic Interaction: Not present as ammonia is non-ionic.

Conclusion

• Understanding intermolecular forces helps predict molecular properties like boiling points.
• Listing and identifying intermolecular forces in different molecules provide insights into their behavior and interactions.