Lesson 1-4 Intermolecular Forces

Kinetic Molecular Theory (KMT)

• Matter is composed of tiny particles that are always in motion.

• KMT explains observable properties and behaviors of solids, liquids, and gases.

• It elucidates why matter exists in different phases and how phase transitions occur.

Postulates of Kinetic Molecular Theory

1. Particles in Motion

   • Matter consists of particles constantly in motion.

   • Motion is attributed to kinetic energy.

2. Kinetic Energy and Temperature

   • The kinetic energy of a substance correlates with its temperature.

   • Higher temperatures result in greater molecular speed.

3. Interparticle Space

   • There are spaces between particles, varying with the state of matter.

4. Phase Changes

   • Changes in temperature can induce phase changes in substances.

5. Intermolecular Forces

   • Attractive forces exist between particles (intermolecular forces).

   • Strength of these forces increases as particles get closer together.

States of Matter

• Gaseous State: Molecules are far apart with significant empty space.

• Liquid State: Molecules are close together with minimal empty space.

• Solid State: Molecules are fixed in position, vibrating about fixed spots.

Types of Intermolecular Forces

• Intermolecular forces are crucial in explaining the condensation of gases into liquids and solids.

Comparison of Intermolecular vs. Intramolecular Forces

• Intramolecular Forces:

  • Hold atoms in a molecule together (e.g., chemical bonds).

  • Stabilize individual molecules.

• Intermolecular Forces:

  • Attractive forces between molecules.

  • More influential in liquids and solids than in gases.

Lesson 2: Types of Intermolecular Forces

1. London Dispersion Forces

   • Present between all atoms/molecules; significant in nonpolar ones.

   • Enable condensation of substances like O2, CO2, and noble gases.

2. Dipole-Dipole Forces

   • Attractive forces between polar molecules with dipole moments.

   • Strength increases with larger dipole moments.

3. Hydrogen Bonding

   • A stronger subset of dipole-dipole interactions between polar molecules containing hydrogen and highly electronegative elements (N, O, F).

4. Ion-Dipole Forces

   • Interactions between ions and polar molecules.

   • Crucial for dissolving processes, e.g., NaCl in water.

Summary of Intermolecular Forces

• Different forces involved based on molecular interaction (polar vs. nonpolar).

• Dispersion forces, dipole-dipole forces, hydrogen bonding, and ion-dipole forces are key categories.

Lesson 3: Properties of Liquids

1. Surface Tension

   • Causes liquid surfaces to contract; molecules resist external force due to cohesiveness.

2. Capillary Action

   • Tendency of liquids to rise in narrow spaces due to intermolecular attraction.

   • Two forces involved:

     • Cohesion (attraction between like molecules).

     • Adhesion (attraction between unlike molecules).

3. Viscosity

   • Resistance to flow; influenced by molecular interactions.

   • Measured in centipoise.

4. Vapor Pressure

   • The pressure exerted by vapor in equilibrium with its liquid phase; related to evaporation.

5. Molar Heat of Vaporization

   • Energy needed to vaporize 1 mole of liquid; indicates strength of intermolecular forces.

6. Boiling Point

   • The temperature at which vapor pressure equals external pressure; characteristic of a liquid.

Lesson 4: Properties of Water

1. Boiling and Freezing Points

   • Pure water boils at 100°C and freezes at 0°C.

   • Latent heat is required for phase changes.

2. Specific Heat

   • The heat needed to raise 1 gram of a substance by 1°C.

3. Density of Liquid Water

   • Water is unique; it expands upon freezing, making ice less dense than liquid water.

4. Thermal Properties

   • Water stores/releases more heat than many substances per temperature degree.

5. Heat of Vaporization

   • Significant energy is needed to vaporize water, affecting temperature during evaporation.

6. Power of Hydrogen pH

   • Water can dissociate into hydrogen ions (H+) and hydroxide ions (OH-).