Crystallization
Definition and meaning of Crystallization in chemistry.
Crystallization is the process by which dissolved, molten, or gaseous particles come together to form a solid with a highly ordered, repeating atomic or molecular arrangement called a crystal lattice.
In more detail
It typically begins when a solution becomes supersaturated or a liquid is cooled below its freezing point, driving particles toward the more stable, lower-energy ordered lattice. The process occurs in two stages: nucleation, where a tiny ordered cluster first forms, and crystal growth, where additional particles deposit onto that nucleus. Because the growing lattice strongly favors particles of one specific size, shape, and charge, impurities tend to be excluded, which is why crystallization is a standard technique for purifying solid compounds in the laboratory and industry.
Key facts
| Field | Physical Chemistry |
|---|---|
| Key stages | Nucleation, then crystal growth |
| Common driving force | Supersaturation or supercooling |
| Example crystal | CuSO4·5H2O (copper(II) sulfate pentahydrate) |
Slowly cooling a hot, saturated aqueous solution of copper(II) sulfate produces large, well-formed blue crystals of CuSO4·5H2O as the solution becomes supersaturated on cooling.
Frequently asked questions
How does crystallization differ from precipitation?
Crystallization usually refers to the slow, controlled formation of large, well-ordered crystals (often for purification), while precipitation is the typically rapid formation of an insoluble solid, which may be fine-grained or poorly ordered.
Why does crystallization purify a substance?
The crystal lattice grows by repeating a very specific geometric arrangement, so molecules or ions that do not fit that pattern are largely excluded and left behind in the surrounding solution or melt.