Hydrate

A hydrate is a crystalline compound with water molecules incorporated into its solid structure. The water may occupy fixed sites in the crystal or be coordinated to its constituent ions.

Crystal structure: The three-dimensional arrangement of atoms, ions, or molecules in a crystalline solid. A hydrate’s defining water molecules occupy positions within an ordered crystal.
Dehydration reaction: A chemical process that removes water from a substance. Heating often converts a hydrate into a less hydrated form or an anhydrous solid.
Copper(II) sulfate pentahydrate: A blue crystalline copper salt containing five water molecules per formula unit. Its visible color change on dehydration makes it a familiar indicator for water.
Anhydrous compound: A compound that contains no water as part of its chemical composition. It is the water-free form often produced when a hydrate loses its crystal water.
Water of crystallization: Water molecules incorporated in a crystalline solid in a definite or variable proportion. This is the water component that distinguishes hydrates from anhydrous crystals.
Efflorescence: The loss of water of crystallization from a hydrate exposed to air. Some hydrates release water spontaneously when ambient humidity is low.
Gypsum: A mineral composed of calcium sulfate dihydrate, CaSO₄·2H₂O. Heating gypsum partially removes its crystal water to produce plaster of Paris.
Clathrate hydrate: A crystalline solid in which water molecules form cages that trap guest molecules. This specialized hydrate traps molecules in water cages rather than simply hosting water in another solid’s lattice.
Coordination complex: A central atom or ion bonded to surrounding molecules or ions called ligands. Some hydrate water molecules bind directly to metal ions as ligands.
Deliquescence: The uptake of atmospheric moisture by a solid until it dissolves in the absorbed water. Unlike water loss from efflorescence, moisture uptake can destabilize a hydrate through dissolution.

Linked from 32 pages