Intermolecular Forces & Related Concepts – GenChem 2 Lesson 2

Vocabulary flashcards reviewing key terms and definitions related to intermolecular forces, kinetic molecular theory, and phase changes from the lecture.

Intermolecular Forces of Attraction (IMFA)

Collective name for the attractive forces that act between molecules: London dispersion, dipole–dipole, ion–ion, ion–dipole, and hydrogen bonding.

London Dispersion Forces (LDFs)

The weakest IMFA, produced by temporary fluctuations in electron density; present between all electrically neutral molecules, polar or non-polar.

Temporary (Instantaneous) Dipole

Momentary uneven distribution of electrons in an atom or molecule that creates a short-lived partial charge.

Induced Dipole

Dipole created in a neighboring atom or molecule in response to an instantaneous dipole’s electric field.

van der Waals Forces

General term for weak intermolecular attractions, specifically London dispersion and dipole–dipole forces, named for Johannes van der Waals.

Dipole (Polar Molecule)

Molecule possessing two opposite partial charges due to unequal electronegativity of its bonded atoms.

Dipole–Dipole Interaction

Moderately strong IMFA between the partial positive end of one polar molecule and the partial negative end of another.

Ion–Ion Interaction

Electrostatic attraction between oppositely charged ions, i.e., cations (+) and anions (–).

Cation

Positively charged ion produced by loss of one or more electrons.

Anion

Negatively charged ion produced by gain of one or more electrons.

Ion–Dipole Interaction

Attraction between an ion and a polar molecule; common in solutions of ionic compounds dissolved in polar solvents (e.g., NaCl in water).

Hydrogen Bonding

Special strong dipole–dipole force that occurs when hydrogen is covalently bonded to fluorine, oxygen, or nitrogen and interacts with F, O, or N on another molecule.

Hydrogen Bond Donor

Molecule that provides the partially positive hydrogen atom in a hydrogen bond.

Hydrogen Bond Acceptor

Atom or molecule (usually F, O, or N with a lone pair) that attracts the hydrogen in a hydrogen bond.

FON Rule

Mnemonic indicating that H must be bonded to Fluorine, Oxygen, or Nitrogen for hydrogen bonding to occur.

Kinetic Molecular Theory (KMT)

Model stating that all matter consists of particles in constant motion; particle speed (kinetic energy) increases with temperature.

Temperature (KMT Definition)

Measure of the average kinetic energy of the particles in a substance.

Freezing Point Depression

Lowering of a liquid’s freezing point when a solute (e.g., salt) disrupts crystal formation.

Boiling Point Elevation

Increase in a liquid’s boiling point caused by addition of a non-volatile solute such as salt.

Deposition

Phase change in which a gas transforms directly into a solid without passing through the liquid state.

Predicting IMFA

Determine molecular polarity: all molecules exhibit LDFs; polar molecules also show dipole–dipole forces; molecules with H–F, H–O, or H–N exhibit hydrogen bonding.

Phase States of Matter

Solid: closely packed, vibrating particles; Liquid: particles in close contact, able to slide past; Gas: widely separated, fast-moving particles.

Average Kinetic Energy

Energy proportional to temperature; increases as temperature rises, influencing particle motion and phase.

Effect on Boiling/Melting Points

Stronger intermolecular forces lead to higher boiling and melting points compared to substances of similar molar mass.