Intermolecular Forces

• Definition: Attractive forces between molecules that determine the state of matter (solid, liquid, gas) at a given temperature.

• Types of Intermolecular Forces:

  • Dispersion Forces:
  • Weak forces caused by temporary shifts in electron density in electron clouds.
  • Dipole-Dipole Forces:
  • Attractions between oppositely charged regions of polar molecules.
  • Hydrogen Bonds:
  • Special dipole-dipole attractions involving hydrogen bonded to highly electronegative atoms (F, O, N) with lone pairs.

• Examples of Intermolecular Forces:

  • Water's hydrogen bonds allow it to be liquid at room temperature, unlike similar nonpolar compounds (e.g., methane) that are gases.
  • Ammonia (NH₃) forms hydrogen bonds, but the O-H bonds in water (H₂O) are stronger due to oxygen's higher electronegativity than nitrogen.