Intermolecular Forces

1. Intermolecular Forces (a) Particles in solid (b) Particles in liquid (c) Particles in gas

2. Properties of Solids, Liquids, and Gases Property Solid Liquid Gas Shape Has definite shape Takes the shape of Takes the shape the container of its container Volume Has a definite volume Has a definite volume Fills the volume of High densities High densities the container Low densities Bonding Ionic, Metallic, Covalent Covalent Covalent Arrangement of Fixed, very close Random, close Random, far apart, Particles Crystalline or amorphous Collisions Interactions BetweenVery strong forces: Strong forces: Essentially none Particles (i.e. Melting point, (i.e. Boiling point, malleability, ductility, Surface Tension, conductivity…) Viscosity, Vapor pressure…)

3. Liquid Surface Tension • molecules minimize • their surface area (“skin”) • molecules at surface • interact only with molecules • in the interior of liquid • surface molecules • subjected to inward force, • so surface is under tension • surface tension increases • with increasing intermolecular • forces H2O(l) Water Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 31

4. Liquid Viscosity • resistance of a liquid to flow • greatest in substances with • strong intermolecular forces, • which hinder flow • longer molecules higher • viscosity than shorter ones H2O(l) Water Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 31

5. Acetone

6. Gasoline (Hexane)

7. Corn Syrup

8. Motor Oil

9. Molasses

10. - + + - - + - + - + + - - + + - Repulsion Attraction Intermolecular ForcesDispersion (London Force) • (a) Interaction of any two atoms or molecules. Electrons unevenly distributed. Creates instantaneous (temporary dipole). Polarization increases with size. • (b) interaction of many dipoles. WEAKEST forces! - + - + Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 442

11. - + + - - + - + - + + - - + + - Repulsion Attraction Intermolecular Forces Dipole-Dipole • (a) Interaction of two polar molecules. Polar molecules have permanent dipoles from electronegativity difference. Higher melting and boiling points due to stronger IM forces. • (b) interaction of many dipoles in a liquid. - + - + Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 442

12. H H O O H H Intermolecular Forces Hydrogen Bonding • Strong intermolecular forces of attraction between molecules containing fluorine, oxygen, or nitrogen bonded to hydrogen • Results from large electronegativity difference and small atomic size of hydrogen Hydrogen bonds Chemical Bonds Chemical Bonds Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 442

13. GeH4 Boiling Points of Covalent Hydrides H2O 0 H2Te H2Se SnH4 H2S SiH4 CH4 50 100

14. H O H O H H C C H H H H Ethanol and Water are Soluble ‘Like dissolves like’ Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 469

15. “Oil and Water Don’t Mix” • Oil is nonpolar • Water is polar “Like dissolves like”, nonpolar dissolves nonpolar, nonpolar does not dissolve polar Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 470

16. = Cl- = Na+ Dissolving of solid NaCl Na+ Cl- Na+ Cl- Cl- salt Na+ NaCl solid NaCl (aq)

17. Na+ ions Water molecules Cl- ions SolubilityDissolving of NaCl in Water NaCl(s) + H2O  Na+(aq) + Cl-(aq)

18. H H H H H H H H H H H H H H H H H H H H H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H H H H H H H H H H H H H H H H H H H H H H H O Cl H H H H Cl H H H H H Cl H H H H Cl H H H H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H H H H Cl H H H H Cl H H H H H Cl H H H Cl H H H H H H H H H H-O-C-C-O-C-C-O-C-C-O-C-C-O-H H H H H H H H H Lava Lamp Polar mixture Water Polyethylene glycol Nonpolar mixture Chlorinated paraffin Paraffin from kerosene Heat transfer coil Bulb gives heat and light

19. Evaporation (Vaporization) • Molecules must have sufficient energy to break IM forces. • Molecules at the surface break away and become gas (“volatility”). • Only molecules with enough KE escape. • Breaking IM forces absorbs energy. Evaporation is endothermic. • Rate of evaporation increases with increasing surface area, increasing temperature, and weaker IM forces

20. Condensation • Forming IM forces from gas to liquid • Condensation is exothermic because energy is released. • Dynamic equilibrium: rate of vaporization equals rate of condensation (gas molecules above liquid becomes constant). • Vapor pressure: partial pressure of gas in dynamic equilibrium with liquid • Vapor pressure increases with increasing temperature and weaker IM forces

21. Boiling point: temperatureat which the vapor pressure of a liquid is equal to the pressure above it.Normal boiling point is boiling point at atmospheric pressure Microscopic view of a liquid near its surface Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 446

22. Formation of a bubble is opposed by the pressure of the atmosphere Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 452

23. Effect of Pressure on Boiling Point

24. Heating Curves • Temperature Change • change in KE (molecular motion) • depends on heat capacity • Phase Change • change in PE (molecular arrangement) • temperature remains constant • Heat Capacity • energy required to raise the temp of 1 gram of a substance by 1°C (q = mC∆T) Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

25. Heating Curve for Water vaporization E gas D 100 condensation C liquid melting Temperature (oC) B 0 A freezing solid Heat added LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 487

26. Gas - KE Boiling - PE  Liquid - KE  Melting - PE  Solid - KE  Heating Curves 140 120 100 80 60 40 Temperature (oC) 20 0 -20 -40 -60 -80 -100 Energy

27. Heating Curves • Heat of Fusion (Hfus) • energy required to melt 1 gram of a substance at its melting point. Breaking intermolecular forces in the solid. Water = 6.02 kJ/mol (@ M.P.) • Heat of Vaporization (Hvap) • energy required to vaporize 1 gram of a substance at its boiling point. • usually larger than Hfus (requires complete separation of molecules) • higher temperatures = lower (Hvap) Water = 40.7 kJ/mol (@ B.P.) Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

28. Calculating Energy Changes - Heating Curve for Water 140 DH = mol xDHvap DH = mol xDHfus 120 100 80 ∆H = mCgasDT 60 40 Temperature (oC) 20 ∆H = mCliquidDT 0 -20 -40 -60 ∆H = mCsolidDT -80 -100 Energy

29. Specific Heat Capacities Tro's "Introductory Chemistry", Chapter 3

30. Energy Changes Accompanying Phase Changes Gas Vaporization Condensation Sublimation Deposition Energy of system Liquid Melting Freezing Solid Brown, LeMay, Bursten, Chemistry2000, page 405

31. Phase Diagram Water • Show the phases of a substance at different temperatures and pressures.

32. Phase Diagram of CO2

33. Solids • Ionic – Giant lattice of ions, strong electrostatic attractions between metal and nonmetal, strong bonds, high melting points, crystalline, poor conductors except in molten and aqueous states (NaCl, KBr…) • Discrete Covalent – Groups of atoms covalently bonded by sharing electrons between two nonmetals/metalloids, weaker bonds than ionic, IMFs with relatively low melting points (except very large polymers), soft, poor conductors (plastics, wax…) • Giant Covalent – Massive structures of atoms bonded through network covalent bonds, very strong bonds with very high melting points, hard/rigid, poor conductors (graphite (carbon), diamond (carbon), SiO2, Si…) • Metallic – Closely packed array of atoms or ions with “sea” of free moving electrons, all metals and alloys (mixtures), stronger bonds than covalent but weaker than ionic, high melting points, malleable/ductile/shiny, very good conductors (Cu, Na…)

38. Molecular Structure of Ice Hydrogen bonding Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 455

41. Natural Polymers Cellulose is a macromolecule composed of individual sugar molecules (glucose) that are bonded together to give molecular weights in the millions. Cellulose is the basis for cotton and rayon fibers as well as the structural support in plants Starch Cellulose RNA and DNA Chitin Cotton Natural Rubber

42. Synthetic Polymers • “Everyday Polys” • Polypropylene • Polystyrene • Polyvinyl Chloride • Polyester • Polyethylene Polyvinyl chloride Polypropylene Polystyrene Polyethylene