Final answer:
An unsaturated solution contains less solute than the maximum amount it can hold, allowing more solute to be dissolved if added. Saturated solutions have reached their solubility limit and will have excess solute if more is added. Dilute and concentrated solutions describe the solute concentration levels.
Step-by-step explanation:
An unsaturated solution is one which contains less solute than the maximum amount that the solvent can dissolve at a given temperature and pressure. This means that if additional solute is added, it will continue to dissolve until the solution reaches its saturation point. In contrast, if a solution is saturated, any added solute will not dissolve, indicating that the solution already contains the maximum amount of solute that can be dissolved in the solvent. Valence shell electrons generally do not play a direct role in solution saturation, but understanding the valence shell is crucial in other areas of chemistry, such as chemical bonding and reactions.
To determine if a solution is unsaturated, one can simply add more solute to see if it dissolves. If it does, the original solution was unsaturated. This can be contrasted with a saturated solution, which may have excess undissolved solute sitting at the bottom, illustrating that no more solute can dissolve. A dilute solution has a low solute concentration, while a concentrated solution has a high solute concentration, regardless of whether the solution is saturated or unsaturated.