London Dispersion Forces
Weakest IMF; arise from temporary dipoles. Present in ALL molecules. Strength increases with molar mass and surface area.
Example: I2 is solid at room temp due to strong LDF from large electron cloud.
Adaptive
Learn Intermolecular Forces
Read the notes, then try the practice. It adapts as you go.When you're ready.
Session Length
~17 min
Adaptive Checks
15 questions
Transfer Probes
8
Lesson Notes
Intermolecular forces (IMFs) are attractions between molecules that determine physical properties like boiling point, vapor pressure, viscosity, and solubility. London dispersion forces (LDF) arise from temporary dipoles and exist in all molecules.
Dipole-dipole forces occur between polar molecules. Hydrogen bonding is a strong dipole-dipole force involving H bonded to N, O, or F. Ion-dipole forces are strongest in aqueous solutions. This topic covers IMF types, their effect on physical properties, phase diagrams, solutions, and colligative properties for AP Chemistry Unit 3.
You'll be able to:
- Identify London dispersion, dipole-dipole, and hydrogen bonding forces from molecular structure
- Relate intermolecular forces to boiling point, vapor pressure, viscosity, and solubility
- Interpret phase diagrams and predict phase transitions at given T and P
- Calculate colligative properties including boiling point elevation and freezing point depression
- Explain separation of mixtures using differences in intermolecular forces
One step at a time.
Interactive Exploration
Adjust the controls and watch the concepts respond in real time.
Key Concepts
Dipole-Dipole Forces
Attractions between permanent dipoles of polar molecules.
Example: HCl molecules align positive-to-negative end.
Hydrogen Bonding
Strong dipole-dipole force when H is bonded to N, O, or F.
Example: Water has unusually high boiling point due to hydrogen bonding.
Ion-Dipole Forces
Attraction between an ion and a polar molecule. Strongest IMF in solutions.
Example: Na+ surrounded by water molecules (hydration).
Vapor Pressure
Pressure exerted by vapor in equilibrium with its liquid. Inversely related to IMF strength.
Example: Diethyl ether has higher vapor pressure than water.
Phase Diagram
Graph of pressure vs temperature showing solid, liquid, and gas regions, with triple and critical points.
Example: Water phase diagram: negative slope solid-liquid line (anomalous).
Colligative Properties
Properties depending on number of solute particles, not identity: boiling point elevation, freezing point depression, osmotic pressure.
Example: Salt lowers freezing point of water (road de-icing).
Viscosity
Resistance to flow. Increases with stronger IMFs and larger molecules.
Example: Honey (strong H-bonds, large molecules) is more viscous than water.
Explore your way
Choose a different way to engage with this topic — no grading, just richer thinking.
Explore your way — choose one:
Concept Map
See how the key ideas connect. Nodes color in as you practice.
Worked Example
Walk through a solved problem step-by-step. Try predicting each step before revealing it.
Adaptive Practice
This is guided practice, not just a quiz. Hints and pacing adjust in real time.
Small steps add up.
What you get while practicing:
- Math Lens cues for what to look for and what to ignore.
- Progressive hints (direction, rule, then apply).
- Targeted feedback when a common misconception appears.
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