Intermolecular Forces Intramolecular forces chemical bonds H2O (l)  H2 (g) + ½ O2 (g) 935 kJ Intermolecular forces between molecules H2O (s)  H2O (l)  H2O (g) 6.02 kJ 40.7 kJ Heating Curve phase transitions s  l  g x-axis = time heat added y-axis = T

ice at -20oC  add heat  increase T increase KE motion T heat  s  l ice 0oC  water 0oC heat capacity raise T 1 g 1oC at 0oC temperature stops rising change T of water phase transition temperature 100oC increase PE breaking IMF phase transition Intermolecular Forces l  g

Intermolecular Forces heat of fusion melting strength of IMF heat of vaporization IMF electrostatic Q1 Q2 big charges d2 small distances Ionic bonds metals and non-metals cations anions + - Na+ Cl- salts high m.p.

Intermolecular Forces ion-dipole + or - +or - polar compounds IMF electrostatic Q1 Q2  lower strength d2 NaCl + H2O  Na+ (aq) + Cl- (aq) + + - - + -

Intermolecular Forces dipole-dipole +or - +or - IMF electrostatic 1 2 smaller charges d2 neutral but polar compounds CH3Cl  = 2 D CH3CN  = 3.9 D b.p. = 249 K b.p. = 355 K

Intermolecular Forces special dipole-dipole hydrogen bonding - + F-H F + - F-H F O-H + O - + N-H N - N H O H O H O H O H N H

Intermolecular Forces non-polar compounds London Dispersion Forces “instantaneous” dipole moments - + - + He e- e- e- b.p. He 2 -269 small short lived short distance Ne 10 -246 strength increases polarizibility Ar 18 -186 36 -152 e- further from nucleus Kr Xe 54 -107 Rn 86 -62

Intermolecular Forces non-polar compounds London Dispersion Forces “instantaneous” dipole moments size shape C5H12 pentane neo-pentane b.p. = 309 K b.p. = 282 K

Intermolecular Forces non-polar compounds London Dispersion Forces “instantaneous” dipole moments all compounds and atoms have LDF HBr HCl b.p. = 206 K b.p. = 189 K stronger LDF more polar 18 e- 36 e-

Surface Tension water on wax imbalance in IMF minimize surface surface tension  IMF cohesion adhesion glass is Si and O H-bond to water capillary action

Phase changes Vapor pressure Liquid-Vapor Equilibrium liquid gas evaporation Vapor pressure depends on T depends on IMF