chapter6_the chemical bonds and molecular structures幻灯片资料.ppt

Dispersion force/London force (instantaneous dipole- instantaneous induced dipole force) nonpolar molecule – nonpolar molecule polar molecule – nonpolar molecule polar molecule –polar molecule Distribution of Van der Waals’ Forces Molecular Orientation force Induction force Dispersion force Total force Ar 0.000 0.000 8.5 8.5 CO 0.003 0.008 8.75 8.75 HI 0.025 0.113 25.87 26.00 HBr 0.69 0.502 21.94 23.11 HCl 3.31 1.00 16.83 21.14 NH3 13.31 1.55 14.95 29.60 H2O 36.39 1.93 9.00 47.31 Dispersion/London exist between all molecules. Except substance with high polarity or hydrogen bonds, exemplified by H2O, dispersion force is more significant than orientation and induction forces. Summary of Van der Waals’ Forces --- Orientation force, induction force and dispersion force Van der Waals’ Forces exist in all molecules Van der Waals’ Forces are very weak compared with chemical bonds No directionality and saturability The interaction distance is only several pm Dispersion force is more significant than orientation and induction forces. Effect of Van der Waals’ Forces on physical properties He Ne Ar Kr Xe Radius Deformation Dispersion force Intermolecular force m.p. and b.p. ? 457 387 I2 332 266 Br2 238 172 Cl2? 85 53.6? F2? b.p./K m.p./