Intermolecular forces and observable properties
≈ 48 minIntermolecular forces and observable properties
Intermolecular forces act between particles; they are different from the covalent bonds inside a molecule. London dispersion forces occur between all atoms and molecules because electron distributions fluctuate. Permanent dipole-dipole attractions occur between polar molecules. Hydrogen bonding is a particularly strong attraction when hydrogen is bonded to nitrogen, oxygen or fluorine and is attracted to a lone pair on a nearby molecule. Stronger attractions generally require more energy to separate particles, so they can raise boiling point, melting point and viscosity while lowering volatility. Compare particles of similar size before using force type alone as an explanation.
Work it through
Compare methane and water. Both are molecular substances, but methane is non-polar and has only London forces. Water is polar and each molecule can form hydrogen bonds. More energy is needed to separate water molecules, explaining water's much higher boiling point. The O-H covalent bond inside water is not the hydrogen bond between water molecules.
Mastery target
Identify the dominant attraction in a stated substance and use a particle-level explanation to predict a relative physical property.
Which force is the most important intermolecular attraction between CH₄ molecules?
Name the key chemistry term from Intermolecular forces and observable properties that best fits the explanation and visual model.
Which substance is expected to have the higher boiling point, and why?
Which statement corrects a common misunderstanding in Intermolecular forces and observable properties?