1. IM Forces Section 10.1

2. States of Matter

3. Forces Between Particles in Solids and Liquids Ionic compounds –Attractive forces between oppositely charged ions hold ionic compounds together. –Ionic bonds are the strongest interparticle force. –Smaller the ion and the larger the charge on the ion the stronger the attractive forces among the ions

4. Ionic Bonding

5. Forces Between Particles in Solids and Liquids Forces between molecular compounds –Intermolecular (IM) forces between molecules attract molecules to each other in the liquid and solid state. IM forces are very weak as compared to ionic or covalent bonds

6. IM Forces Three types of IM Forces 1.Dipole-dipole force 2.Hydrogen “bonding” 3.London dispersion forces See pages 440-442

7. Interparticle Forces and Physical Properties The stronger the attractive forces between particles in a liquid or solid, the –Higher the: Melting point Boiling point Surface tension Viscosity –Lower the: Vapor pressure

8. IM Forces Dipole-dipole forces –Attractive forces between oppositely charged dipoles. –Dipole-dipole forces are found between polar compounds. The more polar the compound the stronger the dipole-dipole force.

9. IM Forces Hydrogen “bonds” –Attractive force between a  + H bonded to an O, N, or F and a  - O, N, or F generally on another molecule. Really a relatively strong dipole-dipole force –Hydrogen bonding is the strongest of the IM forces. –H bonding is very important in water and in many biological molecules.

10. Hydrogen “bond” is a weak attractive force between a  + hydrogen and a  -  O, N, or F in a second polar bond

11. London Dispersion Forces London Dispersion force –Very weak and short-lasting attractive forces between temporary dipoles See figure 10.5 –Weakest of the IM forces

12. London Dispersion Forces London Dispersion forces –Found between all molecules in liquid/solid state. Of greatest significance in nonpolar molecules as it’s the only IM force between nonpolar molecules –The larger the molecule the stronger the dipersion forces.

13. Dispersion Forces Occur between every compound and arise from the net attractive forces amount molecules which is produced from induced charge imbalances The magnitude of the Dispersion Forces is dependent upon how easily it is to distort the electron cloud. The larger the molecule the greater it’s Dispersion Forces are.

14. Dispersion Forces and Molecular Shape Elongated molecules have higher dispersion forces than compact molecules Ringed structures have higher dispersion forces than straight chain molecules. –Consider: Hexane Cyclohexane 2,2 – dimethyl butane

15. Interparticle Forces Weakest to Strongest: Intermolecular forces – all relatively weak London dispersion forces Dipole-dipole force Hydrogen Bonding Ionic bond - BY FAR THE Strongest: - not an IM Force

16. Properties of Liquids Freezing and boiling point Surface tension Capillary action Viscosity  Which are directly related to the strength of the IM forces present between molecules?

17. Change of State Normal Freezing/Melting point –temperature at which the liquid and solid state co-exist at 1 atm pressure Normal boiling point –temperature at which the liquid and gaseous state co-exist at 1 atm pressure Predict the relative BP of: –Methane, acetone, methanol, ethanol, NaCl

18. Surface Tension Surface tension –Resistance of a liquid to increase its surface area –Measure of the energy needed to break the IM forces at the surface

19. Capillary Action Capillary action –Spontaneous rising of a liquid in a narrow tube Related terms: –Cohesive forces – attractive forces among like molecules –Adhesive forces – attractive forces among dislike molecules

20. See Figure 10.7, page 444 Concave meniscusConvex meniscus Adhesion > CohesionCohesion > adhesion

21. Viscosity Viscosity – resistance of a liquid to flow –Highly viscous liquids are thick (syrupy) –Consider relative viscosity of: Propanol Glycerol

22. Graphite Layers of ringed carbon structures –Each C is bonded to 3 other C –Each C is sp 2 hybridized

23. Diamond A diamond is a gigantic molecule, each C atom is bonded to 4 other C atoms Each C is sp 3 hybridized

24. A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. Phase Diagram of Water 11.9

26. CH 11: Properties of Solutions 1.Describing Solutions – concentration units 2.Energetics of solution formation 3.Colligative Properties of solutions BP elevation FP depression Osmotic pressure Vapor Pressure

27. Terms Solution – homogeneous mixture Solvent – generally the larger component of the solution –Determines the physical state of the solution Solute – generally the smaller component of the solution –Solute is dispersed in the solvent

28. Solution Composition Concentrated solution – relatively large amount of solute Dilute solution – relatively small amount of solute

29. Solution Composition Unsaturated solution –solution with less than the maximum amount of solute that will normally dissolve at a given temperature Saturated solution - solution with maximum amount of solute that will normally dissolve at a given temperature

30. Solution Composition Super-saturated solution - solution with more than the maximum amount of solute that will normally dissolve at a given temperature

31. Concentration Units Molarity (M) = moles solute/Liters solution Molality (m) = moles solute/kg solvent Mass % = Mass solute/mass solution x100%  Mole fraction (   ) = moles A/total moles

32. Practice! Start by writing definitions for the concentration units M = m = Mass % = Mole fraction =

33. Starting with Molarity Solution: –3.75 M H 2 SO 4 solution with a density of 1.23 g/mL Calculate: –Mass % –Molality –mole fraction of H 2 SO 4

34. Starting with Masses Solution: –A solution is made by combining 66.0 grams of acetone (C 3 H 6 O) with 146.0 grams of water. –Solution has a density of 0.926 g/mL Calculate: –Molarity – need volume of solution –Mass % –Molality –Mole fraction of acetone

35. Starting with Mass % Solution: –35.4 % H 3 PO 4 –Density of 1.20 g/mL Calculate: –Molarity –Molality –Mole fraction of H 3 PO 4

36. Starting with Molality Solution: –2.50 m HCl solution –Density of 1.15 g/mL Calculate: –Molarity – need _______ –Mass % –Mole fraction of HCl

37. Solution Formation Formation of a solution involves 3 steps 1.Separate the solute particles expand the solute 2.Separate the solvent particles Expand the solvent 3.Form the solution –Solute and solvent interact

38. Solution Formation Each step of solution formation involves energy and has a  H.  H 1 = energy needed to separate the solute  H 2 = energy needed to separate the solvent  H 3 = energy released when solution forms

39. Solution Formation  H solution  H 1 +  H 2 +  H 3 Solutions form when the  H solution is a small value – see page 492

40. Factors Impacting Solubility Structure – like dissolves like –#38 on page 520

41. Factors Impacting Solubility Pressure –Pressure has little impact on the solubility of liquids and solids –Pressure has a significant impact on the solubility of gases in a liquid The higher the pressure of gaseous solute above a liquid the higher the concentration of the gas in the solution

42. Henry’s Law Henry’s Law: C = kP C = Concentration of dissolved gas k = solution specific constant P = partial P of the solute gas above the solution No calculations required. Page 494

43. Temperature and Solubility Temperature has variable effects on the amount of solid that will dissolve in an aqueous solution! –See figure 11.6 page 496 Solutes do dissolve more rapidly at higher temperatures

44. Temperature and Solubility The solubility of a gas in water decreases as temperature increases. –See figure 11.7 on page 496 –Thermal pollution – read the story on page 497 when you get a chance

45. Vapor Pressure of Solutions See Raoult’s Law on page 498 solventsolventP solution =  solvent P 0 solvent

46. Colligative Properties Colligative properties –properties of a solution that depend upon the amount of dissolved solute, not the identity of the solute. Freezing point depression Boiling point elevation Osmotic Pressure Note: I will be weaving section 11.7 and the van’t Hoff factor (i) into my consideration of these properties and not consider it separately.

47. Colligative Properties  FP = K f m i  BP = K b m i See page 505 for needed constants

48. 1.Calculating the bp or fp of a solution 2.Calculating the molar mass of a solute from fp or bp data

49. Osmotic Pressure Osmotic Pressure (  ) is often used to determine the molar mass of large biological molecules –See figure 11.17 on page 508  = MRTi