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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Intermolecular forces

Attractions between separate molecules (or atoms): London dispersion forces, dipole–dipole forces and hydrogen bonding. They are far weaker than the covalent bonds within molecules, and they are what boiling or melting a molecular substance overcomes.

Molecular solidDiscrete molecules, each held together by strong covalent bonds, packed in a crystal and attracted to each other only by weak intermolecular forces (dotted lines), as in ice, dry ice (solid CO₂) or iodine.strong covalent bonds within molecules,weak intermolecular forces between them (dotted)low melting; soft (ice, dry ice, I₂)

Strong covalent bonds inside each molecule; weak forces between them.

Example

Boiling water separates whole HX2O\ce{H2O} molecules: about 41 kJ/mol is needed to vaporize water at 100 °C, far less than the 463 kJ/mol needed to break a single O–H bond.

See alsoLondon dispersion forcesDipole–dipole forcesHydrogen bondingBoiling point