In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. These surrounded solute particles then move away from the solid solute and out into the solution. The mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution usually has the state of the solvent when the solvent is the larger fraction of the mixture, as is commonly the case. One important parameter of a solution is the concentration, which is a measure of the amount of solute in a given amount of solution or solvent. The term "aqueous solution" is used when one of the solvents is water. Characteristics A solution is a homogeneous mixture of two or more substances. The particles of solute in a solution cannot be seen by the naked eye. By contrast, particles may be visible in a suspension. A solution does not cause beams of light to scatter. By contrast, the particles in a suspension can cause Tyndall scattering or Rayleigh scattering. A solution is stable; solutes will not precipitate unless added in excess of the mixture's solubility, at which point the excess would remain in its solid phase, referred to as hypersaturation. The solute from a solution cannot be separated by filtration (or mechanically). It is composed of only one phase. Types Homogeneous means that the components of the mixture form a single phase. Heterogeneous means that the components of the mixture are of different phase. The properties of the mixture (such as concentration, temperature, and density) can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids, or solids. One or more components present in the solution other than the solvent are called solutes. The solution has the same physical state as the solvent. Gaseous mixtures If the solvent is a gas, only gases (non-condensable) or vapors (condensable) are dissolved under a given set of conditions.