Kinetic Molecular Theory and Intermolecular Forces

• The Kinetic Molecular Theory (KMT) is based on the assumption that all states of matter have component molecules that possess kinetic energy.
• The amount of kinetic energy, motion, and arrangement of molecules differs for gases, solids, and liquids.

KMT Assumptions on Shape and Volume

• Gases have no definite shape or volume; they fill any container.
• Liquids have definite volume but no definite shape.
• Solids have definite shape and volume.

Intermolecular Forces

• London dispersion forces
• Dipole-dipole forces
• Ion-dipole forces
• Hydrogen bonding

London Dispersion Forces (LDF)

• LDF explain attractions between nonpolar molecules, which can have temporary dipoles.
• Dispersion forces increase with molecular mass and decrease with distance.

Dipole-Dipole Forces

• These forces involve the attraction of bond dipoles in different molecules.
• Bond dipoles result from unequal sharing of electrons in covalent bonds.

Ion-Dipole Forces

• These forces occur when polar molecules are attracted to ions.
• Positive poles attract anions, and negative poles attract cations.
• An example is dissolving NaCl in H₂O.

Hydrogen Bonding

• A hydrogen bond is a bridge between two highly electronegative atoms (F, O, or N), with one covalently bonded to hydrogen.
• Molecules with hydrogen bonded to F, O, or N have significant hydrogen bonding ability.

Properties of Liquids

• Surface tension
• Viscosity
• Capillary action
• Evaporation
• Cooling effect of evaporation
• Vapor pressure
• Boiling point

Surface Tension

• Surface tension is the force causing surface molecules to tighten their hold, creating a membrane-like effect.
• Substances with strong attractive forces have high surface tensions.
• It decreases as temperature increases.

Viscosity

• Viscosity measures a liquid's resistance to flow.
• Cooking oil is more viscous than gasoline due to stronger London dispersion forces.
• Glycerol is more viscous than rubbing alcohol.
• High viscosity liquids are "thick," while low viscosity liquids are "thin" or "mobile."

Capillary Action

• This is the spontaneous rising of a liquid in a narrow tube.
• It results from cohesive forces within the liquid and adhesive forces between the liquid and the container walls.

Evaporation

• Evaporation is the escape of molecules from the liquid's surface, indicating molecular motion.

Vapor Pressure

• When a liquid vaporizes in a closed container, the space above becomes saturated, establishing equilibrium between the liquid and vapor.
• At equilibrium, evaporation and condensation rates are equal.

Boiling Point

• The temperature at which a liquid's vapor pressure equals the external pressure.