Honors Chemistry - Intermolecular Forces(IMF)

Intermolecular Forces (IMFs)

Attractive forces between separate molecules.

Intramolecular Forces

Forces within a molecules(covalent, ionic metallic bonds); they are much stronger than IMFs and hold atoms together.

London Dispersion Forces (LDF)

Weak, temporary attractions that arise from instantaneous dipoles caused by fluctuating electron clouds; present in all molecules, especially large or heavy ones.

Dipole‑Dipole Forces

Attractions between the permanent partial positive end of one polar molecule and the partial negative end of another; strength depends on polarity and electronegativity differences.

Hydrogen Bonding

A strong dipole‑dipole interaction that occurs when hydrogen is covalently bonded to N, O, or F and is attracted to a lone‑pair on another electronegative atom

Melting Point (MP)

The temperature at which a solid becomes a liquid

Boiling Point (BP)

The temperature at which a liquid turns to gas.

Cohesion

The attractive force between like molecules (e.g., water‑water); gives rise to surface tension.

Adhesion

The attractive force between unlike substances (e.g., water‑glass); essential for capillary action.

Capillary Action

The ability of a liquid to flow in narrow spaces without external forces, driven by the balance of cohesion and adhesion.

Surface Tension

The tendency of a liquid’s surface to contract to the smallest possible area due to cohesive forces among surface molecules.

Viscosity

A measure of a fluid’s resistance to flow

Polar Molecule

molecule with an uneven distribution of electron density, creating permanent partial charges (dipole).

Non‑polar Molecule

A molecule with a symmetric electron distribution, lacking a permanent dipole

Partial Positive/Negative Charge

Regions of a molecule where electron density is respectively lower or higher, creating dipoles.

Electronegativity

An atom’s tendency to attract electrons in a bond

Temporary Dipole

A fleeting separation of charge within a molecule caused by momentary electron movement, the source of LDFs.

Lone Pair

A pair of non‑bonding electrons on an atom

Molecular Size

Larger molecules have more electrons and surface area, enhancing LDF strength and often raising boiling points.

Physical Properties (as influenced by IMFs)

Observable traits like melting/boiling points, viscosity, surface tension, and capillary action that change with the type and strength of intermolecular forces.