Crystal water

Crystal water consists of water molecules incorporated into a crystalline solid in a definite proportion. These molecules occupy structural sites in the crystal rather than merely wetting its surface.

Hydrate: A compound containing water molecules as part of its chemical composition. Crystal water is the defining feature of hydrated crystalline compounds.
Water: A polar molecule composed of two hydrogen atoms bonded to one oxygen atom. Crystal water retains the identity and composition of water molecules.
Copper(II) sulfate pentahydrate: A blue crystalline compound with formula CuSO₄·5H₂O. Its five water molecules per formula unit provide a classic visible example of crystal water.
Anhydrous compound: A compound containing no water of crystallization in its specified solid form. An anhydrous solid is the water-free counterpart often produced by dehydrating a hydrate.
Anhydrite: The mineral form of anhydrous calcium sulfate, CaSO₄. It can form when gypsum loses its two waters of crystallization.
Coordination complex: A central atom or ion bonded to surrounding molecules or ions called ligands. Water molecules can bind metal ions directly as ligands within a crystal.
Chemical formula: A symbolic notation showing the elements and proportions in a substance. Hydrate formulas use a dot and a water count to express crystal-water proportions.
Gypsum: A mineral composed of calcium sulfate dihydrate, CaSO₄·2H₂O. Its crystal water distinguishes gypsum from anhydrous calcium sulfate.
Adsorption: The accumulation of atoms or molecules on a material's surface. Surface-adsorbed water is not incorporated at defined sites in the crystal lattice.
Phase transition: A change between distinct physical states or structural phases of matter. Dehydration can produce a new crystalline phase rather than merely a lighter sample.

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