Which of the following pure substances has the stronger London forces?
London dispersion forces are present between all molecules even if there are also dipole-dipole attractions or hydrogen bonds. London dispersion forces depend on the polarizability of a molecule, which in turn depends on the number of electrons and the volume over which they are spread. The greater the number of electrons and their volume, the greater the polarizability and the greater the strength of the London dispersion forces. a. Ethane b. Oxygen c. Sulfur dioxide d. Methane – Each has the same number of electrons, but methane has them spread over a larger volume, and so is more polarizable. Ammonia has a higher boiling point, but that is because NH3 exhibits dipole-dipole attraction in addition to London dispersion forces. Ammonia is polar, methane is nonpolar.
