A suspension is a heterogeneous mixture in which particles are dispersed throughout a liquid or gas medium, but they are large enough to eventually settle or separate over time due to gravity or other external forces. In contrast, a colloid is a type of mixture in which particles are dispersed evenly throughout a medium, but they are small enough to remain suspended indefinitely due to the Brownian motion of the surrounding liquid or gas molecules.
The particles in a suspension are usually much larger and heavier than those in a colloid, and they are not held in place by any sort of intermolecular or electrostatic forces. Therefore, they are more susceptible to settling or separating out of the mixture over time. In addition, the particles in a suspension can be easily separated from the liquid or gas medium by filtration or sedimentation, which is not possible with colloids.
On the other hand, the particles in a colloid are small enough to be affected by Brownian motion, which is the random movement of molecules in the surrounding liquid or gas. This constant movement keeps the particles in suspension, preventing them from settling or separating out of the mixture. Furthermore, colloids can exhibit some unique properties, such as Tyndall scattering or the ability to pass through a semipermeable membrane, that distinguish them from both solutions and suspensions.