CHEM 16 APE PART 3

• Solid


  Molecules that are held together rigidly in position<|>Molecules that do not freely move<|>Less empty space than in liquids; incompressible
• Liquid


  Difficult to compress than gases<|>Denser under normal conditions<|>Molecules that are held together by more than one type of attractive forces
• Gas


  Molecules separated by large distances<|>Huge empty spaces between molecules; readily compressed<|>Lack strong forces between molecules
• Kinetic Molecular Theory


  • Matter is made up of atoms and molecules that are always moving
  • Any form or type of matter hold kinetic energy and move around in random directions
  • High temperatures → high energy
  • Low temperatures → less energy
  • The more kinetic energy, the faster the movement
• Solids


  Particles hardly move and hold a regular pattern because the kinetic energy is low, and they are tightly packed
• Liquids


  Particles have a higher kinetic energy than those in solids and hence, they are free to move
• Gases


  Particles have the highest kinetic energy because they are dispersed and move around freely
• Phase changes


  1. Transformations from one state of a matter to another

  2. Occurs when energy (usually in the form of heat) is added or removed from a substance

  3. Characterized by changes in molecular order
• Vaporization


  Liquid changes to the gaseous state, which happens in the boiling point of a liquid
• Evaporation


  Liquid changes to the gaseous state below its boiling point
• Condensation


  1. Gas molecules condense to become liquid

  2. Occurs when a molecule strikes the liquid surface and becomes trapped by intermolecular forces in the liquid
• Melting


  Transformation of a solid to liquid
• Freezing


  Transformation of a liquid to solid
• Freezing point/Melting point


  Temperature at which solid and liquid phases co-exist in equilibrium
• Latent heat


  Amount of energy needed to change the phase a certain mass of a substance to a unit mass of material
• Steel strut near a ship's furnace

  • Change in temperature: 355°C
  • Increase in length: 7.8 x 10^-3 m
• Ice added to water in a cooler

  • Temperature of the water when it comes to equilibrium: 3.03°C
• Intermolecular force


  Attractive forces between molecules
• Intramolecular force


  Attractive forces that hold atoms together in molecule
• Intermolecular forces are much weaker than intramolecular forces
• Types of intermolecular force

  • Ion-Ion Force (Strongest)
  • Ion-Dipole Force
  • Hydrogen Bonding
  • Dipole-Dipole Interaction
  • Dispersion Forces (weakest)
• Ion


  Charged atoms or molecules
• Dipole


  Molecule that has both positive and negative regions that are separated with each other
• Electronegativity


  Ability of an atom to attract shared electrons how much electrons wants to be near an element
• Polar molecules


  Molecules that possess dipole moments, which arise from differences in electronegativities
• Characteristics of polar vs non-polar molecules

  • Polar: One slightly positive end and one slightly negative end, central atom with lone pair, terminal atoms not symmetrically arranged

  Non-polar: Compounds having the same atom / monoatomic molecules, central atoms without lone pairs, all terminal atoms symmetrically arranged
• Ion-ion force


  Attractive force between positive and negative ions, also known as ionic bonds, strongest intermolecular force
• Ion-dipole force


  Force that attracts an ion (cation or anion) and a polar molecule to each other, strength depends on charge/size of ion, magnitude of dipole moment, and size of molecule
• Hydrogen bonding


  Special type of dipole-dipole interaction between hydrogen atom in a polar bond and an electronegative O, N, or F atom, quite large average strength
• Dipole-dipole interaction


  Attractive forces between polar molecules, larger the dipole moment the larger the force
• Dispersion forces


  Attractive forces that arise from temporary dipoles induced in atoms/molecules due to proximity of an ion or polar molecule, present in all molecules
• Intermolecular forces influence rate of evaporation, boiling point, and solubility
• Rate of evaporation


  Evaporation requires input of energy (enthalpy of vaporization), greater the forces of attraction between molecules the greater the energy needed
• Boiling point

  As temperature rises, molecules gain kinetic energy, boiling point reached when molecules have sufficient kinetic energy to escape forces of attraction, stronger IMFs = higher boiling point
• Solubility

  Like dissolves like - polar solute and polar solvent, non-polar solute and non-polar solvent
• Surface tension


  Amount of energy required to stretch or increase the surface of a liquid by a unit area, liquids with strong IMFs have high surface tension
• Capillary action


  Tendency of a liquid to rise in narrow tubes or be drawn into small openings due to attraction between liquid molecules and material
• Cohesive force


  Intermolecular forces between molecules of a liquid
• Adhesive force


  Interaction between a liquid and solid surface
• Meniscus


  Curved surface of a liquid, can be concave or convex depending on relative cohesive and adhesive forces