Intermolecular Forces and Properties of Liquids – Chapter 11

Vocabulary flashcards covering key terms and definitions related to intermolecular forces, molecular interactions, and liquid properties from Chapter 11.

Intermolecular Forces (IMFs)

Attractive or repulsive forces between molecules, ions, or atoms that are not covalently bonded; collectively called van der Waals forces.

van der Waals Forces

General term for all intermolecular forces excluding covalent and ionic bonding; includes dipole–dipole, dipole–induced dipole, and London dispersion forces.

Coulomb’s Law

Equation (F = −k q1 q2 / d²) describing the electrostatic force between two charges; magnitude increases with larger charges and shorter distance.

Ion–Ion Attraction

Strong electrostatic force between oppositely charged ions in ionic solids, leading to high melting and boiling points.

Ion–Dipole Force

Attractive force between an ion and a polar molecule; strength increases with ion charge, smaller ion size, and larger dipole moment.

Dipole–Dipole Force

Attraction between the positive end of one polar molecule and the negative end of another polar molecule.

Hydrogen Bond

Special, strong dipole–dipole attraction where H is covalently bonded to N, O, or F and forms a bridge to another electronegative atom.

Dipole–Induced Dipole Force (Debye Force)

Attractive force where a permanent dipole in one molecule induces a temporary dipole in a nearby non-polar molecule.

Induced Dipole–Induced Dipole Force

Also called London dispersion force; temporary attractions arising from synchronized electron motions in neighboring non-polar molecules.

London Dispersion Force

Weak, universal IMF caused by momentary fluctuations in electron density; strength increases with molar mass and polarizability.

Polarizability

Ease with which an electron cloud can be distorted to form an induced dipole; larger, more diffuse clouds are more polarizable.

Hydration Enthalpy (ΔhydrH⁰)

Heat released when an ion is solvated by water molecules; becomes more exothermic with higher ion charge and smaller ionic radius.

Enthalpy of Vaporization (ΔvapH⁰)

Energy required to vaporize 1 mole of a liquid at its boiling point; endothermic and proportional to IMF strength.

Enthalpy of Condensation

Heat released when 1 mole of vapor condenses to liquid; numerically equal but opposite in sign to ΔvapH⁰.

Equilibrium Vapor Pressure

Pressure exerted by a vapor in dynamic equilibrium with its liquid at a given temperature.

Volatility

Measure of a liquid’s tendency to evaporate; high volatility corresponds to high vapor pressure and weak IMFs.

Normal Boiling Point

Temperature at which a liquid’s vapor pressure equals 760 mm Hg (1 atm).

Clausius–Clapeyron Equation

ln P = −ΔvapH⁰ / (R T) + C; relates vapor pressure to temperature and allows calculation of ΔvapH⁰.

Critical Temperature (Tc)

Highest temperature at which a substance can exist as a liquid, regardless of applied pressure.

Critical Pressure (Pc)

Minimum pressure required to liquefy a gas at its critical temperature.

Supercritical Fluid

State of matter above Tc and Pc where liquid and gas phases merge; combines gas-like viscosity with liquid-like density.

Surface Tension

Energy required to increase a liquid’s surface area by one unit; caused by unequal IMF on surface molecules.

Capillary Action

Rise or fall of a liquid in a narrow tube due to competition between adhesive and cohesive forces.

Meniscus

Curved surface of a liquid in a container; concave for liquids that wet glass (e.g., water), convex for those that do not (e.g., mercury).

Cohesive Forces

Intermolecular attractions between like molecules within a liquid.

Adhesive Forces

Intermolecular attractions between unlike molecules, such as a liquid and a solid surface.

Viscosity

Resistance of a liquid to flow; increases with stronger IMFs and decreases with higher temperature.

States of Matter

Physical forms of matter—solid, liquid, gas—distinguished by particle spacing and IMF influence.

Hydrogen-Bond Network in Water

Each H₂O molecule can form four H-bonds, giving water high boiling point, high specific heat, and lower-density ice.

Dipole Moment (Debye, D)

Quantitative measure of molecular polarity; product of charge magnitude and separation distance.

Like Dissolves Like

Rule of thumb stating polar solvents dissolve polar solutes, and non-polar solvents dissolve non-polar solutes due to compatible IMFs.

Polar Molecule

Molecule with an uneven distribution of charge resulting in a permanent dipole moment.

Non-Polar Molecule

Molecule with a symmetrical charge distribution and no permanent dipole moment.

Debye (unit)

Unit (D) used to express dipole moments; 1 D ≈ 3.34 × 10⁻³⁰ C·m.

Hydrated Salt

Ionic compound containing specific numbers of water molecules bound in its crystal lattice, often via ion–dipole interactions.

Specific Heat Capacity of Water

4.184 J g⁻¹ K⁻¹; unusually high due to extensive hydrogen bonding, moderating Earth’s climate.

Polarizability Trend

In homologous series, polarizability—and thus dispersion forces—increases with increasing molar mass and electron count.

Dynamic Equilibrium (Liquid–Vapor)

Condition where rate of evaporation equals rate of condensation, resulting in constant vapor pressure.