142. How do the boiling points of R—Cl, R—Br and R—I show variations? Justify your answer.

i) There is increase in the boiling points with increasing molar masses of the members of the same family of compounds. Since, there is increase in the molar masses from R—Cl to R—I, therefore, there is increase in their boiling points also. Thus, the boiling point of R—I is greater than the boiling point of R—Br and the boiling point of R—Br is greater than that of R—Cl. Thus, boiling points follow the order R—I > R—Br > R—Cl.


ii) The Van der Waals interactions between the molecules of R—I are stronger than that between R—Br molecules. Therefore, more energy and thus high temperature is required to cause the boiling point of R—I as compared to R—Br. Again, the molecular interactions due to Van der Waals forces in R—Br are stronger as compared to that in R—Cl. Therefore, the boiling point of bromoalkane is higher than the boiling point of chloroalkane.