Colloid
Definition and meaning of Colloid in chemistry.
A colloid is a mixture in which microscopically dispersed particles, typically 1 to 1000 nanometers across, are distributed throughout a continuous medium without settling out or dissolving as individual ions or molecules.
In more detail
Colloidal particles are too large to form a true solution but too small to settle under gravity like a suspension, so they remain permanently dispersed due to constant collisions with solvent molecules (Brownian motion). Colloids scatter visible light, producing the Tyndall effect, which distinguishes them from true solutions. They are classified by the physical states of the dispersed phase and dispersion medium, giving types such as sols, emulsions, foams, and aerosols. Colloidal stability depends on particle charge and surface interactions, which prevent aggregation (coagulation) into larger clumps.
Key facts
| Particle size range | 1-1000 nm |
|---|---|
| Field | Physical Chemistry |
| Key test | Tyndall effect (light scattering) |
| Common types | Sol, emulsion, foam, aerosol, gel |
Milk is a colloid: microscopic droplets of fat and protein micelles are dispersed throughout water, scattering light and giving milk its opaque white appearance rather than settling or dissolving.
Frequently asked questions
How does a colloid differ from a solution?
In a true solution the dissolved particles are individual ions or molecules (under about 1 nm) and do not scatter light, while colloidal particles are larger aggregates that scatter light visibly (Tyndall effect) yet still stay suspended indefinitely.
How does a colloid differ from a suspension?
Suspension particles are larger than about 1000 nm and settle out over time under gravity, whereas colloidal particles remain dispersed because Brownian motion keeps them from settling.