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Understanding Intermolecular Forces in States of Matter

Explore intermolecular forces in solids, liquids, and gases. Identify similarities and differences. Learn about types of intermolecular forces and their impact on properties like boiling point and vapor pressure. Practice problems and calculations included.

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Understanding Intermolecular Forces in States of Matter

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  1. Section 10.1 Intermolecular Forces Based on the enthalpy values and what you know of solids, liquids, and gases, which two states of matter are most similar? Which is most unique? DHfus = 6.02 kJ/mol DHvap = 40.7 kJ/mol Answer Now

  2. Liquids and Solids Chapter 10

  3. Types of Intermolecular Forces • Dipole-Dipole • Molecules must have dipole • Opposites attract • Attractions weaken as distance between dipoles increase. • Hydrogen Bonding • Type of Dipole-Dipole • Between H and any highly EN atom. (ie: F, N, O) • Extremely strong attraction

  4. Types of Intermolecular Forces, 2 • London Dispersion Forces • Noble Gases and Non-Polar Molecules • Temporary Dipoles form • Sometimes called Induced Dipole Forces • Weaker than Dipole-Dipole • In molecules with large atoms, dispersion forces are often more important than dipole forces.

  5. Properties and Intermolecular Forces • What properties do intermolecular forces affect? • Boiling Point • Freezing Point • Vapor Pressure • Surface Tension • Capillary Action • Viscosity

  6. Identify the most important types of intermolecular forces present in each of the following substances: In each of the following group of substances, pick the one what has the given property and justify your answer: Practice Problems • Highest boiling point: HCl, Ar, or F2 • Highest freezing point: H2O, NaCl, or HF • Lowest Boiling Point: CH4, CH3CH3, or CH3CH2CH3 • Ar • HCl • CH4 • CO • NaNO3

  7. Vapor Pressure • Vapor Pressure of a liquid occurs when some particles are vaporized just above the surface of the liquid. • Volatile liquids have higher vapor pressures • REMEMBER: Patmosphere = Pvaporization + PHgColumn • The heat of vaporization (DHvap) is the amount of heat required to change 1 mole of liquid to gas. • Endothermic values

  8. Vapor Pressure Relationships Vapor Pressure Molar Mass Vapor Pressure Temperature Intermolecular Forces Vapor Pressure

  9. Vapor Pressure Calculations lnPvap = -(DHvap/R)(1/T) Use 8.314 J/Kmol for R. The vapor pressure of water at 25oC is 23.8 torr and the DHvap of water is always 43.9 kJ/mol. Calculate the vapor pressure of water at 50oC. Try Me Problem

  10. Heating Curve • When a solid is heated, it will absorb energy (increase temp) until it begins to melt. • At melting point and at boiling point, the two states of matter are present. • No change in temperature occurs until all particles are converted.

  11. Phase Diagrams • Relate the temperature, pressure, and state of matter for a substance. • Triple Point is the point at which all three states of matter are present. • Critical Point is the last temperature and pressure combination at which it is possible to condense particles to a liquid.

  12. Phase Diagram of Water Melting Evaporation Sublimation

  13. Myth Fact What IS Boiling Point?

  14. Special Cases • Superheated liquid: A liquid that is heated so rapidly that it is actually at a temperature that is above the boiling point, but has not evaporated. • Supercooled liquid: A liquid that is cooled so rapidly that it is actually at a temperature that is below the freezing point, but has not solidified. UNSTABLE !

  15. Section 10.3 Structures and Types of Solids • Ionic solids • Molecular solids • Atomic solids • All types of solids form crystal lattices. • The smallest repeatable unit inside a crystal lattice is a unit cell.

  16. Unit Cells • Simple cubic: one atom at each vertex. Polonium metal Basic format Binary Compound

  17. Unit Cells, 2 • Body centered cubic: at each vertex and in the center. Uranium metal Basic Format Binary Compound

  18. Unit Cells, 3 • Face centered cubic: at each vertex and in the center of each face. Also called Cubic Closest Packing structure because each new layer of atoms nests into the holes from the layer below. Basic Format Binary Compound

  19. Hexagonal Close Packed: each atom in the second layer lays in a dimple between the atoms in the sandwiching layers. Unit Cells, 4 Basic Format Binary Compound

  20. Carbon as diamond Physical Properties Structure Bonding Carbon as graphite Physical Properties Structure Bonding Section 10.5 Atomic Solids

  21. Section 10.6 Molecular Solids • Covalent bond length within molecule is shorter than the distance between attracted molecules. • Low melting points, relatively weak IMF’s • Examples of molecules that form Molecular Solids: • Water • Carbon Dioxide • Any other covalently bonded molecule

  22. Section 10.7 Ionic Solids • The large ions define the shape of the crystal lattice. Smaller ions fit in the holes between the larger ions. • Stable • High Melting Point • Strong Intermolecular Forces (because ions have good dipole moments!) • Examples of things that form ionic solids: • NaCl • CsCl • Any other ionic compoud

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