How are crystals formed when water evaporates?

Answer 1

If we consider something like salt dissolved in water, we know that the salt (NaCl), which has an ionic bond, will exist in the water in solution in the form of ions. There will be ions of sodium, which is Na+ and chlorine, which is Cl- in the water. This is because the water molecules will pull the salt molecules apart into those ions to create the solution. When the water evaporates, the ions will no longer remain in solution. The water molecules are leaving the solution in the form of water vapor. Soon, there won't be enough water left for the salt ions to remain in ionic form. We'll have what is called a saturated solution, and, at that temperature and pressure, the water will be able to hold in solution only the amount of salt present. As evaporation continues with water molecules changing state into vapor, sodium and chlorine ions will be recombining to form NaCl molecules (salt). As more water evaporates, additional NaCl ions will form and will attach themselves to the existing salt molecules. The salt molecules will be forming a definite shape, and that shape will be the characteristic shape of a salt crystal (which is in the shape of a cube). The manner that crystals will form when water that has dissolved them evaporates will be similar.