Intermolecular Forces

Types of intermolecular forces, properties

Intermolecular Forces

Intermolecular forces (IMFs) are attractions between molecules. Three main types: London/dispersion forces (weakest, all molecules), dipole-dipole forces (polar molecules), hydrogen bonds (strongest IMF, H bonded to N, O, or F). IMFs determine boiling point and viscosity.

Example

Comparing IMFs

CH4 (methane): non-polar, only London forces, very low boiling point (-161 C). HCl: polar, dipole-dipole, higher boiling point (-85 C). H2O: hydrogen bonding, much higher boiling point (100 C).

Note

Exam Tip

Do not confuse intermolecular forces (between molecules) with chemical bonds (within molecules). Chemical bonds are much stronger. When a substance boils, IMFs are overcome — bonds remain intact.

Key Vocabulary

Intermolecular forceA force of attraction between molecules

Hydrogen bondA strong IMF between molecules containing H bonded to N, O, or F

Dipole-dipole forceAn IMF between polar molecules with permanent dipoles

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Intermolecular force

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