APCE Intermolecular Forces & Properties

Question 1

Which type of intermolecular force is responsible for the attraction between polar molecules?

Accepted Answer

Dipole-dipole interactions.

Answer

Dipole-dipole interactions are attractive forces that occur between the permanent dipoles of polar molecules. The partially positive end of one polar molecule is attracted to the partially negative end of an adjacent polar molecule. These forces are stronger than London dispersion forces but generally weaker than hydrogen bonds.

Question 2

What is the strongest type of intermolecular force in water?

Accepted Answer

Hydrogen bonding.

Answer

Water (H₂O) exhibits hydrogen bonding because it contains hydrogen atoms directly bonded to a highly electronegative oxygen atom. Hydrogen bonds are a particularly strong type of dipole-dipole interaction, occurring when hydrogen is bonded to fluorine, oxygen, or nitrogen. These strong attractions are responsible for many of water's unique properties, including its relatively high boiling point.

Question 3

What is the effect of increasing intermolecular forces on the boiling point of a substance?

Accepted Answer

The boiling point increases.

Answer

Boiling point is the temperature at which a liquid's vapor pressure equals the surrounding atmospheric pressure, allowing it to transition into a gas. To overcome the attractive forces holding liquid molecules together and allow them to escape into the gas phase, energy is required. Stronger intermolecular forces mean more energy is needed to separate the molecules, thus resulting in a higher boiling point.

Question 4

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

Accepted Answer

H₂O (Water).

Answer

Water (H₂O) has the highest boiling point among the given options because it exhibits strong hydrogen bonding, a particularly potent type of intermolecular force. H₂, N₂, and Cl₂ are nonpolar or weakly polar molecules that primarily rely on weaker London dispersion forces for attraction. The extensive hydrogen bonding in water requires significantly more energy to overcome, leading to its much higher boiling point.

Question 5

What is the primary factor that affects the strength of London dispersion forces?

Accepted Answer

The size of the molecule and the number of electrons.

Answer

London dispersion forces (LDFs) arise from temporary, induced dipoles caused by the instantaneous movement of electrons. The strength of LDFs increases with the number of electrons in a molecule because a larger electron cloud is more easily distorted (more polarizable). This means larger molecules with more electrons will experience stronger London dispersion forces.

AP Practice Test

AP Practice Test

APCE Intermolecular Forces & Properties