Intermolecular Forces Intramolecular forces chemical bonds Intermolecular forcesbetween molecules H 2 O (l)  H 2 (g)+ ½ O 2 (g) H 2 O (s)  H 2 O (l)  H 2 O (g) phase transitions Heating Curve x-axis y-axis = time = T heat added s  l  g 935 kJ 6.02 kJ 40.7 kJ

ice at -20 o C heat  add heat  increase T increase KEmotion heat capacity raise T1 g1oC1oC at 0 o Ctemperature stops rising phase transition temperature increase PE breaking T  IMF s  l ice 0 o C  water 0 o C change T of water 100 o C phase transition l  g Intermolecular Forces

heat of fusion melting heat of vaporization strength of IMF IMFelectrostaticQ1Q1 Q2Q2 d2d2 Ionic bondsmetals and non-metals cationsanions -+ Na + Cl - big charges small distances salts high m.p.

Intermolecular Forces IMFelectrostaticQ1Q1 Q2Q2 d2d2 ion-dipole + or -  + or  - polar compounds  lower strength NaCl + H2OH2O  Na + (aq) + Cl - (aq) + -- -- - ++ ++

Intermolecular Forces IMFelectrostatic 11 22 d2d2 dipole-dipole  + or  - neutral but polar compounds CH 3 ClCH 3 CN  = 2 D  = 3.9 D smaller charges b.p. = 249 Kb.p. = 355 K

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

Intermolecular Forces non-polar compounds “instantaneous” dipole moments He -- ++ small short lived short distance strength increases e - further from nucleus size He Ne Ar Kr Xe Rn e-e- b.p. London Dispersion Forces polarizibility

Intermolecular Forces non-polar compounds “instantaneous” dipole moments London Dispersion Forces sizeshape pentane neo-pentane C 5 H 12 b.p. = 309 K b.p. = 282 K

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

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