Which of the following substances should have the highest boiling point?

Which of the following substances should have the highest boiling point?

A) Kr B) N2 C) Cl2 D) CCl4 E) CH3Cl

Solution: Boiling point depends on intermolecular forces (forces between molecules). The stronger the intermolecular forces, the higher the boiling point.

If we see an element on its own such as Kr, or a diatomic element such as N2 or Cl2, we can recognize these as nonpolar. CCl4 is a nonpolar molecule as well because it is symmetrical and the dipoles on the bonds will cancel one another. Nonpolar molecules have London dispersion intermolecular forces which are the weakest. CH3Cl is not a symmetrical molecule and is polar. It will have dipole-dipole intermolecular forces. Dipole-dipole intermolecular forces are stronger than London dispersion and will result in a higher boiling point, making choice E the correct answer choice.

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