Intermolecular Forces and Physical Properties
Forces between molecules
Types of intermolecular forces
Intermolecular forces are weaker than chemical bonds but strongly influence physical properties. The main types are London dispersion forces, dipole-dipole interactions, and hydrogen bonding; ion-dipole forces are especially important in solutions.
Force hierarchy
Property relationships
Stronger intermolecular forces generally raise boiling point, melting point, and viscosity, while lowering volatility. Solubility follows the principle "like dissolves like": polar solutes tend to dissolve in polar solvents, and nonpolar solutes in nonpolar solvents.
Which substance is most likely to have the highest boiling point, assuming similar molar mass?
Ammonia can hydrogen bond, giving it stronger intermolecular attractions than the others listed.
Correct answer:
What kind of intermolecular force exists between all molecules?
All molecules experience temporary induced dipoles, so dispersion forces are universal.
Correct answer: London dispersion forces
Comparing boiling points
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1
Step 1: Identify molecular size and shape.
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2
Step 2: Determine whether the molecule is polar.
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3
Step 3: Check for hydrogen bonding.
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Step 4: Compare overall intermolecular force strength.
Solubility clue
If a solute can form strong attractions with the solvent, mixing is more favorable and the substance is more likely to dissolve.
Why does dissolve better in hexane than in water?
Iodine and hexane are both nonpolar, so their intermolecular interactions are more compatible.
Correct answer: Because both are nonpolar