Structure of Ionic Crystals
Table: Types of ionic crystal with description
Crystal structure type
Number of formula units per unit cell
Rock salt (NaCl) type
It has fcc arrangement in which ions occupy the corners and face centres of a cube while ions are present at the body and edge of centres.
Halides of Li, Na, K, Rb, AgF, AgBr, NH4Cl, NH4Br, NH4I etc.
Zinc blende (ZnS) type
It has ccp arrangement in which ions form fcc and each ion is surrounded tetrahedrally by four ions and vice versa.
Fluorite (CaF2) type
It has arrangement in which ions form fcc with each ions surrounded by ions and each ions by 4Ca2+ ions.
Here negative ions form the ccp arrangement so that each positive ion is surrounded by 4 negative ions and each negative ion by 8 positive ions
Caesium chloride (CsCl) type
It has the bcc arrangement with at the body centre and ions at the corners of a cube or vice versa.