Unit II – Intermolecular Forces: Vocabulary Review

A set of vocabulary flashcards covering key terms and definitions from the Unit II lecture on intermolecular forces, including types of forces, their effects on physical properties, and related molecular concepts.

Intermolecular Forces (IMF)

Attractive forces that act between separate molecules or ions and influence physical properties such as boiling point, melting point, and solubility.

Kinetic Energy (of particles)

Energy of motion that tends to keep particles apart in gases, liquids, and solids.

Attractive Forces (between particles)

Intermolecular attractions that draw particles together, opposing their kinetic energy.

Gas – Characteristic Properties

Widely separated particles in rapid, random motion that expand to fill their container.

Liquid – Characteristic Properties

Particles held close by attractive forces; definite volume, takes the shape of its container, more dense than gases.

Solid – Characteristic Properties

Particles packed in a fixed, ordered arrangement with extremely strong intermolecular forces and minimal space between particles.

Covalent Bond

Intramolecular bond where atoms share valence electrons; much stronger than any intermolecular force.

Polar Covalent Bond

Bond in which two atoms share electrons unequally, producing partial charges (commonly when bonding involves N, O, F, Cl, or Br).

Non-polar Covalent Bond

Bond in which two identical or similarly electronegative atoms share electrons equally, resulting in no permanent dipole.

Instantaneous (Temporary) Dipole

Momentary uneven electron distribution in an atom or molecule that can induce attraction with neighboring particles.

London Dispersion Forces

Weak attractions arising from synchronized instantaneous dipoles in all atoms and molecules; only intermolecular force present in non-polar substances.

Polarizability

Ease with which an electron cloud is distorted; increases with molar mass and leads to stronger dispersion forces.

Dipole-Induced Dipole Force (Debye Force)

Attractive interaction where a polar molecule induces a dipole in a nearby non-polar molecule.

Dipole-Dipole Force

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

Hydrogen Bond

Special dipole-dipole attraction between H bonded to highly electronegative F, O, or N and a lone pair on F, O, or N in another molecule.

Tetrahedral Hydrogen-Bond Network (Water)

Structure allowing each H₂O molecule to form four hydrogen bonds, giving water unusually high BP, MP, Cp, and ΔH°vap.

Molar Mass Effect on Dispersion

Within similar molecules, larger molar mass → larger electron cloud → stronger dispersion forces.

Enthalpy of Vaporization (ΔH°vap)

Heat required to convert one mole of liquid to gas; increases as intermolecular forces strengthen.

Vapor Pressure

Pressure exerted by a vapor in dynamic equilibrium with its liquid; decreases as intermolecular forces strengthen.

Dynamic Equilibrium (Liquid ↔ Gas)

State where the rate of evaporation equals the rate of condensation in a closed system.

Boiling Point

Temperature at which a liquid’s vapor pressure equals external (atmospheric) pressure.

Normal Boiling Point

Boiling point measured when external pressure is exactly 1 atm.

Relationship: IMF vs Vapor Pressure

Stronger intermolecular forces → lower vapor pressure → higher boiling point.

Relationship: IMF vs Boiling Point

Substances with stronger intermolecular forces require more energy to boil, thus have higher boiling points.

Hierarchy of IMF Strength

Hydrogen bonding > Dipole-dipole > Dipole-induced dipole > London dispersion (for comparable molecules).

Dispersion-Only Molecules

Non-polar molecules like C₈H₁₈ (octane) or C₅H₁₂ (pentane) that rely solely on London dispersion forces.

Polar Molecule

Molecule with a permanent dipole moment due to uneven charge distribution (e.g., isopropyl alcohol, H₂O).

Non-polar Molecule

Molecule with symmetrical charge distribution and no permanent dipole (e.g., pentane, octane).

Heat Capacity (Cp) of Water

Amount of heat required to raise the temperature of water, unusually high because of extensive hydrogen bonding.

Debye Interaction

Synonym for dipole-induced dipole attraction described by Peter Debye.