Molecules

• Kinetic Molecular Theory of Matter

  All molecules are in motion, most rapid in gases, less rapid in liquid, very slow in solid
• Kinetic Molecular Theory of Solids, Liquids, and Gas

  • Properties of Solid
  • Properties of Liquid
  • Properties of Gas
• Properties of Solid

  • Held by very strong forces of attraction
  • Particles are not free to move
  • Particle vibrate about in fixed positions
• Properties of Liquid

  • Held together by strong forces of attraction
  • Particles are able to slide past one another
• Properties of Gas

  • Free to move
  • Particles are far apart
• Properties comparison

  • Density: Solid - Very high, Liquid - High, Gas - Lower than solid and liquid
  • Diffusibility: Solid - Hardly diffuse at all, Liquid - Diffuse more slowly than gas, Gas - Diffuse more rapidly than solids
  • Compressibility: Solid - Slightly compressible, Liquid - Slightly compressible, Gas - Can be compressed very readily
  • Volume and shape: Solid - Has fixed volume and shape, Liquid - Assumes the shape of the container it occupies, Gas - Has no fixed volume and shape
  • Thermal expansibility: Solid - Expands slightly when heated, Liquid - Expands slightly when heated
• Intramolecular forces

  • Force which keeps molecule together in hands
  • Stronger than intermolecular forces
  • Bond formed within the atom
• Intermolecular Forces

  • Force of attraction between neighboring molecules
  • Forces of attraction caused by the formation of bonds between atoms
  • Responsible for keeping matter in solid or liquid phase
  • Weaker attraction
• Dispersion Forces

  1. Force of attraction between atoms or molecules

  2. Dispersion forces increase with increasing size (top to bottom of PT)

  3. Boiling point increases as dispersion forces increase

  4. As molar mass increases, dispersion forces increase

  5. Molar mass increase, boiling point will also increase
• Properties of Liquids

  • Based on KMT, liquids have the following general properties: Particles slide and roll on top of one another, Particles have limited movement and hence, they flow, Moderately high density and diffusibility, Have fixed volume but no fixed shape
• Surface tension refers to the force that causes the molecules on the surface of a liquid to be pushed together and contract
• Surface tension explains why a drop of liquid is spherical in shape
• The strength of surface tension depends on
• Fusibility


  Have fixed volume but no fixed shape
• Surface tension


  The force that causes the molecules on the surface of a liquid to be pushed together and contract
• Surface tension

  1. Explains why a drop of liquid is spherical in shape

  2. Depends on the intermolecular force of attraction (IMFA)

  3. The stronger the IMFA, the greater the surface tension

  4. Increase in temperature decreases surface tension as temperature breaks the force of attraction

  5. Different for different liquids

  6. Water has high surface tension due to its high ability to form H-bonds
• Viscosity

  The resistance (friction between molecules) of fluids to flow
• Viscosity

  1. A substance that flows readily has low viscosity like water

  2. If the IMFA is strong, the liquid will have high viscosity

  3. The higher the temperature, the lower the liquid’s viscosity as temperature breaks the bonding or increases kinetic energy

  4. Maple syrup is more viscous than water due to more H-bonds causing stronger IMFA
• Vapor Pressure and Boiling Point

  1. Vapor pressure is the force of evaporating molecules

  2. Boiling point is the temperature when the vapor pressure of the liquid is equal to the atmospheric pressure
• Molar Heat of Vaporization

  1. The amount of heat needed to vaporize a given amount of substance at its boiling point

  2. The stronger the IMFA, the higher the heat of vaporization
• Phase changes


  Transformation of matter from one state to another involving the absorption and evolution of heat
• Heating and Cooling Curves of a substance

  1. Increase temperature in melting and evaporation

  2. Decrease temperature in freezing and condensation