Structure Of Ionic Crystals
Category : JEE Main & Advanced
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 \[C{{l}^{-}}\] ions occupy the corners and face centres of a cube while \[N{{a}^{+}}\] ions are present at the body and edge of centres. | Halides of Li, Na, K, Rb, AgF, AgBr, NH4Cl, NH4Br, NH4I etc. | \[N{{a}^{+}}=6\] \[C{{l}^{-}}=6\] | 4 |
| Zinc blende (ZnS) type | It has ccp arrangement in which \[{{S}^{2-}}\] ions form fcc and each \[Z{{n}^{2+}}\] ion is surrounded tetrahedrally by four \[{{S}^{2-}}\] ions and vice versa. | \[CuCl,CuBr,CuI,AgI,BeS\] | \[Z{{n}^{2+}}=4\] \[{{S}^{2-}}=4\] | 4 |
| Type AB2 Fluorite (CaF2) type | It has arrangement in which \[C{{a}^{2+}}\] ions form fcc with each \[C{{a}^{2+}}\] ions surrounded by \[8{{F}^{-}}\] ions and each \[{{F}^{-}}\] ions by 4Ca2+ ions. | \[Ba{{F}_{2}},BaC{{l}_{2}},Sr{{F}_{2}}\] \[SrC{{l}_{2}},Cd{{F}_{2}},Pb{{F}_{2}}\] | \[C{{a}^{2+}}=8\] \[{{F}^{-}}=4\] | 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 | \[N{{a}_{2}}O\] | \[N{{a}^{+}}=4\] \[{{O}^{2-}}=8\] | 4 |
| Caesium chloride (CsCl) type | It has the bcc arrangement with \[C{{s}^{+}}\] at the body centre and \[C{{l}^{-}}\] ions at the corners of a cube or vice versa. | \[CsCl,\,CsBr,\,CsI,\,CsCN,\]\[TlCl,TlBr,TlI\] and \[TlCN\] | \[C{{s}^{+}}=8\] \[C{{l}^{-}}=8\] | 1 |
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