Intermolecular Forces and the Physical properties of Liquids and Solids1212.1 Intermolecular Forces12.2Properties of Liquids12.3Crystal Structure12.4Types of Crystals12.5Amorphous Solids12.6Phase Changes12.7Phase DiagramsIntermolecular ForcesIntermolecular forces are attractive forces that hold particles together in the condensed phases. The magnitude (and type) of intermolecular forces is what determines whether the particles that make up a substance are a gas, liquid, or solid.GasCondensed phasesIntermolecular ForcesIon-ion(between ions)ܧ∝ଵ,ܨ ∝ െభమIon-dipole(between ions and molecules)ܧ∝ଵమ,ܨ ∝ െభయDipole-dipole(between molecules)ܧ∝ଵయ,ܨ ∝ െభరHydrogen bonding (type of dipole-dipole force that is especially strong)London dispersion (occurs between all molecules)ܧ∝ଵల,ܨ ∝ െభళShort-ranged repulsions (when molecules or ions get too close, they “bump” into one another and are repelled by strong short-ranged forces)Interaction Energies and Forces that occur between ions and molecules and other ions and molecules.
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Intermolecular ForcesPermanent dipole momentMore on dipoles….Induced dipole momentis the polarizability and has units of volume.Instantaneous dipole momentδD̅= αE̅D̅Intermolecular ForcesProperties that are affected by the strength of intermolecular forces:•Boiling point•Vapor pressure•Freezing/melting point•Surface tension•Viscosity•Capillary actionThe magnitude of the attractive forces depends on the magnitude of the dipole.Intermolecular ForcesAttractive forces that act between atoms or molecules in a pure substance are collectively called van der Waals forces.Dipole-dipole interactionsare attractive forces that act between polar molecules.Intermolecular Forces