AP Chemistry : Intermolecular Forces
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Example Question #21 : Intermolecular Forces
Which of the following compounds will likely have the highest boiling point, and why?
, because it is the least massive molecule
, because it experiences hydrogen bonding
, because it is the most massive molecule
, because it is the largest molecule
, because it experiences dipole-dipole intermolecular forces.
, because it experiences dipole-dipole intermolecular forces.
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 #21 : Intermolecular Forces
All molecules have what type of intermolecular force?
Hydrogen bonding
London dispersion
Ionic
Covalent
Dipole-dipole
London dispersion
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 #21 : Intermolecular Forces
The stronger the intermolecular forces, __________.
the higher the molar mass
the lower the viscosity
the higher the boiling point
the lower the surface tension
the higher the vapor pressure
the higher the boiling point
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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