AP Chemistry : Intermolecular Forces

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

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Example Question #21 : Intermolecular Forces

Which of the following compounds will likely have the highest boiling point, and why?

Possible Answers:

, because it is the least massive molecule

, because it is the most massive molecule

, because it is the largest molecule

, because it experiences hydrogen bonding

, because it experiences dipole-dipole intermolecular forces.

Correct answer:

, because it experiences dipole-dipole intermolecular forces.

Explanation:

Stronger intermolecular forces (IMFs) hold molecules together, so the strongest IMFs will produce the highest boiling points because more energy will be required to disrupt those bonds and cause a phase shift. 

The answer is that  should have the highest boiling point, due to dipole-dipole interactions. It is the only molecule on the list that experiences these interactions, which are stronger than the IMFs experienced by the others. While it is true that  is the most massive compound in the list, mass has relatively little to do with boiling point, when compared with IMFs. 

 would have the second highest boiling point because, like , its only IMF is induced dipole moments (or London dispersion forces), but because it is a larger molecule than , it will experience more induced dipoles. It does not actually experience hydrogen bonding since none of its hydrogens are bonded to fluorine, oxygen, or nitrogen.

 is the least massive, but again, that has very little to do with the boiling point compared with IMFs. Since it is only experiencing induced dipoles, and is a smaller molecule than , it will have the weakest IMFs and thus the lowest boiling point.

Example Question #22 : Intermolecular Forces

All molecules have what type of intermolecular force?

Possible Answers:

Hydrogen bonding

Ionic

London dispersion

Covalent

Dipole-dipole

Correct answer:

London dispersion

Explanation:

London dispersion forces are weak attractive forces between molecules or atoms. They involve transient induced polarization of atoms and/or electrons that cause two separate atoms or molecules to be attracted to each other.

Example Question #23 : Intermolecular Forces

The stronger the intermolecular forces, __________.

Possible Answers:

the higher the boiling point

the lower the surface tension

the higher the molar mass

the higher the vapor pressure

the lower the viscosity

Correct answer:

the higher the boiling point

Explanation:

The stronger the intermolecular forces, the higher the: boiling point, surface tension, and viscosity; and the lower the vapor pressure. A bigger molar mass doesn't necessarily mean that there are stronger intermolecular forces (that is determined by the type of intermolecular forces present).

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