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Intermolecular and Interparticle Forces

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Beyond the bonds inside a molecule are the weaker intermolecular forces (IMFs) that pull molecules toward each other. From weakest to strongest: London dispersion (present in everything), dipole-dipole (between polar molecules), hydrogen bonding (H bonded to N, O, or F), and ion-dipole (ions in a polar solvent). How strong they are decides melting and boiling points, viscosity, and solubility.

UNIT 3 TOPIC 3.1 • INTERMOLECULAR & INTERPARTICLE FORCES IMF RANKER Compare and rank the three most common intermolecular forces (IMFs). 1. LONDON DISPERSION FORCES (LDF) Cl Cl EXAMPLE: Cl₂ Temporary, instantaneous dipoles Present in ALL atoms and molecules Weakest per interaction ↑ with molar mass / polarizability 2. DIPOLE–DIPOLE FORCES H Cl δ+ δ− EXAMPLE: HCl Attractions between permanent dipoles Between polar molecules (δ+ / δ− ends attract) Stronger than LDF 3. HYDROGEN BONDING O O H H H H δ− δ− δ+ EXAMPLE: H₂O ··· H₂O H bonded directly to N, O, or F + a lone pair on N, O, or F Strongest common IMF (e.g. water, H₂O) WHY IT MATTERS Stronger IMF = more energy needed to separate particles = higher boiling / melting point STRENGTH RANKING (WEAKEST → STRONGEST) 1 LONDON DISPERSION (LDF) 2 DIPOLE–DIPOLE 3 HYDROGEN BONDING CED ANCHOR Hydrogen bonding needs H bonded directly to N, O, or F (+ a lone pair on N/O/F). Stronger IMF → higher boiling / melting point. AP Chemistry · Unit 3 · Properties of Substances & Mixtures
Intermolecular forces ranked. London dispersion acts between all particles; dipole-dipole adds for polar molecules; hydrogen bonding is a strong special case (H bonded to N, O, or F); ion-dipole is stronger still. Their strength sets boiling points and other physical properties.
IMF Ranker · Open the sandbox →

The recurring trap is confusing forces between molecules with the bonds within them: boiling water breaks IMFs, not O–H bonds. Ranking the IMFs correctly, and remembering that every molecule has dispersion forces, is what predicts the physical properties.

The work

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Lesson
Intermolecular Forces ›

London dispersion, dipole-dipole, hydrogen bonding, and ion-dipole form a strength ladder that sets physical properties. The lesson ranks the forces and separates them from bonds, then closes with a ten-scenario check.

Skill check · 10 scenarios
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Diagnostic
10-item topic check ›

Ten items on intermolecular forces: identifying which forces a molecule has, ranking their strength, and telling forces between molecules apart from the bonds within them.

Not started · 10 items · ~15 min
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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions
Diagnostic first