Structure of Ionic Crystals

Structure of Ionic Crystals

Table: Types of ionic crystal with description

Crystal structure type

Brief description

Examples

Co-ordination number

Number of formula units per unit cell

Type AB

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.

4

 

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.

4

Type AB2

Fluorite (CaF2) type

It has arrangement in which  ions form fcc with each  ions surrounded by  ions and each  ions by 4Ca2+ ions.

 

4

Antifluorite type

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

 

4

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.

 and 

1

 

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