Kinetic Molecular Theory and Intermolecular Forces

Kinetic Molecular Theory (KMT)

• KMT is a theory explaining how molecules move in different states of matter (solid, liquid, gas).
• Intermolecular forces are attractive forces between neighboring particles of one or more substances. These forces pull the particles together.
• Kinetic energy keeps particles at a distance and/or moving, and it's dependent on the temperature of the substance. Hotter substances have more kinetic energy.
• Intermolecular forces of attraction vary based on the type of compound.
  • Ionic compounds have forces between oppositely charged particles (ions).
  • Covalent compounds have weaker forces between neighboring molecules, as attraction involves partial charges.

Types of Intermolecular Forces

• London Dispersion Forces:

  • Also called dispersion forces, these are intermolecular forces of attraction between all atoms and molecules.
  • They are the only forces in nonpolar molecules.
  • Uneven electron distribution leads to temporary dipoles in atoms or molecules, causing an attraction to neighboring atoms/molecules.

• Dipole-Dipole Forces:

  • These forces occur between polar molecules.
  • Polar molecules have unequal electron densities, resulting in a dipole (partial positive and partial negative ends).
  • These partial charges attract each other.
  • Forces of attraction are stronger in larger polar molecules due to larger dipoles.

• Hydrogen Bonds:

  • A special type of dipole-dipole interaction.
  • Occurs in molecules with hydrogen bonded to a small, highly electronegative atom (N, O, or F).
  • Strongest of the intermolecular forces.

• Ion-Dipole Forces:

  • Act between an ion (positive or negative) and a polar molecule.
  • The ion is attracted to the oppositely charged end of the polar molecule.