Review IM Forces

1. Review IM Forces Section 10.1

2. 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 ionic bond

3. Forces Between Particles in Solids and Liquids • 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

4. IM Forces Three types of IM Forces • Dipole-dipole force • Hydrogen “bonding” • London dispersion forces See pages 426-428

5. 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

6. 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.

7. IM Forces • Hydrogen “bonds” • Attractive force between a d+ H bonded to an O, N, or F and a d- O, N, or F on another molecule. • Really a relatively strong dipole-dipole force

8. Hydrogen Bonding • Hydrogen bonding is the strongest of the IM forces. • H bonding is very important in water and in many biological molecules.

9. 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

10. 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.

11. Interparticle Forces • Weakest: London dispersion forces Dipole-dipole force Hydrogen Bonding Strongest: Ionic bond

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

13. 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

14. Solution Composition • Concentrated solution • Dilute solution

15. Solution Composition • Unsaturated solution • Saturated solution • Supersaturated solution

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

17. Practice!

18. Solution Formation Formation of a solution involves 3 steps • Separate the solute particles • expand the solute • Separate the solvent particles • Expand the solvent • Form the solution • Solute and solvent interact

19. Solution Formation • Each step of solution formation involves energy and has a DH. DH1 = energy needed to separate the solute DH2 = energy needed to separate the solvent DH3 = energy released when solution forms

20. Solution Formation DHsolution = DH1 +DH2 +DH3 Solutions form when the DHsolution is a small value – see page 492

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

22. 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

23. Henry’s Law: C = kP • No calculations required. Page 494

24. 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

25. 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

26. Vapor Pressure of Solutions • See Raoult’s Law on page 498 • Psolution = csolvent P0solvent

27. 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.

28. Colligative Properties • FP = Kf m i • BP = Kb m i See page 505 for needed constants

29. Calculating the bp or fp of a solution • Calculating the molar mass of a solute from fp or bp data

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