What You Need to Know: A crystal is a solid in which the particles are packed in an ordered, repeated pattern. Precipitation is the process by which a solid falls out of a solution. A precipitate is the solid that precipitates. An evaporite is a precipitate formed by evaporation.
What Does This Mean? Crystals are solids that form when particles join in a regular repeating pattern. Crystals form much like the forming of clusters of soap bubbles with the bubbles representing the particles in a crystal. The bubbles stack together forming a cluster. The addition of each bubble to the bubble cluster represents the stacking of particles in a crystal.
What Does This Have to Do With Growing Crystals? When solids are dissolved in water, they form a solution.
A solution is a homogeneous mixture. A solution is the combination of a solute (what is being dissolved) and a solvent (what the solute is dissolved in) . There is an attractive force between the particles in a solid. However, when dissolved in water (a solvent), the particles of the solid (the solute) separate and spread evenly throughout the solvent particles. Occasionally two solute particles are near each other. There is an attractive force between these solute particles, and they will stick together. Generally, other forces cause them to separate. But if they stay together, they have a greater attractive force than do single particles. As a result a third solute particle sticks to them, then a fourth, and so on, until this cluster of particles can no longer stay dissolved, and it precipitates. The solid precipitate is called a crystal.
|As long as part or all the crystal is surrounded by the solution, two things continue to happen:
1. particles of solute from the solution continue to add to the crystal
2. particles from the crystal continue to dissolve in the solvent
Knowing these two facts, three relationships between the solute particles from the solution that are adding to the crystal and the solute particles that are removed from the crystal when they dissolve in the solvent of the solution.
1. Crystals Grow When:
THE NUMBER OF PARTICLES ADDED > THE NUMBER OF PARTICLES REMOVED
This is read as:
2. Crystals Stop Growing When:
THE NUMBER OF SOLUTE PARTICLES ADDED = THE NUMBER OF SOLUTE PARTICLES REMOVED
This is read as: