Intermolecular Forces and Physical Properties
Types of Intermolecular Forces
Attraction Between Molecules
Intermolecular forces include London dispersion forces, dipole-dipole interactions, hydrogen bonding, and ion-dipole interactions. These interactions are weaker than covalent bonds but crucial for macroscopic behavior.
Force Hierarchy
Which interaction is usually strongest in pure molecular substances?
Among common intermolecular forces in neutral molecular substances, hydrogen bonding is usually the strongest.
Correct answer: Hydrogen bonding
Why do larger nonpolar molecules often have higher boiling points than smaller ones?
More electrons and larger surface area increase polarizability and dispersion interactions.
Correct answer: they have stronger dispersion forces
Structure-Property Relationships
Explaining Trends
Boiling point often increases with stronger intermolecular forces. Viscosity rises when molecules stick together or entangle more easily. Solubility tends to follow the principle that like dissolves like, because favorable interactions must replace existing ones.
Properties and Their Drivers
Boiling point
- Increases with stronger intermolecular forces
- Increases with molecular size in many homologous series
Solubility
- Depends on solvent-solute interactions
- Polar solvents favor polar or ionic solutes
Which compound is most likely to hydrogen bond with water?
Methanol contains an group and can both donate and accept hydrogen bonds.
Correct answer:
State the general rule for predicting whether a substance dissolves in water.
Polar and ionic substances usually dissolve better in polar water than nonpolar substances do.
Correct answer: like dissolves like