Intermolecular Forces & Properties of Liquids – Chapter 11 Review

Vocabulary flashcards summarizing key terms and definitions from Chapter 11 sections on states of matter, intermolecular forces, and liquid properties.

Intermolecular Forces (IMFs)

Attractive forces between separate particles (atoms, ions, or molecules) that influence physical properties of liquids and solids.

van der Waals Forces

Collective term for all intermolecular attractions other than covalent or ionic bonding: dipole-dipole, dipole-induced dipole (Debye), and London dispersion forces.

Coulomb’s Law

Electrostatic force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between them (F = –k q₁q₂ / d²).

Ion–Ion Attraction

Strong electrostatic force between oppositely charged ions; dominates in ionic solids and gives high melting/boiling points.

Ion–Dipole Force

Attraction between an ion and a polar molecule’s permanent dipole; strength increases with ion charge, dipole magnitude, and proximity.

Enthalpy of Hydration (ΔₕydrH°)

Heat released when gaseous ions dissolve in water; becomes more exothermic with higher ion charge and smaller ion radius.

Dipole–Dipole Force

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

Hydrogen Bond

Special strong dipole–dipole attraction in which H bonded to N, O, or F is electrostatically attracted to a lone pair on N, O, or F of a neighboring molecule (5–30 kJ mol⁻¹).

Debye Force

Dipole-induced dipole attraction created when a polar molecule induces a dipole in a non-polar molecule.

London Dispersion Force

Induced dipole–induced dipole attraction arising from instantaneous electron cloud distortions; present in all particles and increase with molar mass and polarizability.

Polarizability

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

Volatility

Tendency of a liquid to evaporate; liquids with weak intermolecular forces and high vapor pressures are more volatile.

Enthalpy of Vaporization (ΔvapH°)

Energy required to convert 1 mol of liquid to vapor at its boiling point; always positive (endothermic).

Enthalpy of Condensation

Energy released when 1 mol of vapor becomes liquid; equal in magnitude and opposite in sign to ΔvapH°.

Vaporization (Evaporation)

Process by which molecules escape the liquid surface to enter the gas phase; requires energy input to overcome IMFs.

Condensation

Process by which gas molecules lose energy and return to the liquid phase; exothermic.

Equilibrium Vapor Pressure

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

Boiling Point

Temperature at which a liquid’s vapor pressure equals the external pressure.

Normal Boiling Point

Boiling temperature of a liquid when the external pressure is 760 mm Hg (1 atm).

Clausius–Clapeyron Equation

ln P = –ΔvapH°/RT + C ; relates vapor pressure to temperature and enables calculation of ΔvapH° from P–T data.

Critical Temperature (Tc)

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

Critical Pressure (Pc)

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

Supercritical Fluid

Single homogeneous phase above Tc and Pc with density like a liquid and viscosity like a gas.

Surface Tension

Energy required to increase a liquid’s surface area by one unit; results from net inward cohesive forces on surface molecules.

Capillary Action

Rise or depression of a liquid in a narrow tube resulting from competing adhesive and cohesive forces.

Meniscus

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

Viscosity

Resistance of a liquid to flow; increases with stronger intermolecular forces or molecular entanglement and decreases with temperature.

Like Dissolves Like

Rule of thumb stating that solubility is favored when solute and solvent have similar polarity and intermolecular forces.

Dipole Moment (Debye)

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

Induced Dipole

Temporary dipole created when an external electric field or neighboring dipole distorts an electron cloud.

Hydration Shell

Arrangement of solvent (commonly water) molecules surrounding and stabilizing an ion via ion–dipole forces.

Hydrogen Bond Donor

Molecule or group containing H bonded to N, O, or F capable of forming a hydrogen bond.

Hydrogen Bond Acceptor

Electronegative atom (N, O, or F) with a lone pair that can attract the H of a neighboring molecule in hydrogen bonding.

Tetrahedral Ice Lattice

Open, hexagonal arrangement in solid water where each H₂O forms four hydrogen bonds, giving ice lower density than liquid water.

Specific Heat Capacity of Water

4.184 J g⁻¹ K⁻¹; unusually high because energy must disrupt extensive hydrogen-bond network to raise temperature.

Polar Molecule

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

Non-Polar Molecule

Molecule with symmetrically distributed charge and no permanent dipole; interactions are dominated by London forces.

Dynamic Equilibrium

Condition in which two opposing processes occur at equal rates, leading to constant macroscopic properties (e.g., liquid ↔ vapor).

Critical Point

Specific combination of critical temperature and critical pressure where liquid and gas phases become indistinguishable.