The attractive forces between molecules of a molecular crystal are

Options

A. relatively weak dipole-dipole intractions
B. relatively weak dispersion forces
C. strong hydrogen bonding
D. any of these

Answer

4

Explanation

Consider naphthalene `(C_(10)H_(8))` as an example. In a naphthalene crystal the nonpolar `C_(10)H_(8)` molecules are held together solely by dispersion forces. Thus we can predict that naphthalene should dissolve readily in nonpolar solvents, such as benzene, but only slightly in water. This is indeed the case.
On the other hand, we find that urea `(H_(2)NCONH_(2))` is much more soluble in water and ethanol than in `C Cl_(4)` or `C_(6)H_(6)`, because it has dipole-dipole interactions, intermolecular hydrogen bonding and the capacity to form hydrogen bonds with water. (The `H` atoms and the `O` and `N` atoms in urea can form hydrogen bonds with `H_(2)O` and `C_(2)H_(5)OH` molecules) Similarly, if we compare the solubilities of molecular `I_(2)`, a nonpolar substance, in water and in carbon tetrachloride, we notice that `I_(2)` is much more soluble in `C Cl_(4)` than in `H_(2)O`.