. Discuss the Classification of Ionic Structures

Best Answer

The classifiation of Ionic Structure are:

1. Rock Salt structure

NaCl exhibits this type of structure. In the rock salt structure, Cl- ions exists in FCC pattern and Na+ ions occupy all octahedral voids. There are 4 effective Na+ ions and 4 effective Cl- ions in a unit cell of NaCl. So, the general formula is Na4Cl4 or NaCl as per the effective ions in a unit cell. The co-ordination number of Na+ ion is 6 and co-ordination number of Cl- ion is also 6. So, the general formula (using co-ordination number of ions) is Na6Cl6 or NaCl.. The other substances having this kind of a structure are halides of all alkali metals except cesium halides and oxides of all alkaline earth metals except beryllium oxide.


2. Zinc Blende Structure

This structure is shown by ZnS. Sulphide ions are face centered cubic position and Zinc is present in alternate tetrahedral voids. Formula is Zn4S4, i.e, ZnS. Coordination number of Zn is 4 and that of sulphide is also 4. Other substance that exists in this kind of a structure is BeO.


3. Fluorite Structures

This structure is exhibited by CaF2. Calcium ions are face centered cubic position and fluoride ions are present in all the tetrahedral voids. There are four calcium ions and eight fluoride ions per unit cell. Therefore the formula is Ca4F8, (i.e, CaF2). The coordination number of fluoride ions is four (tetrahedral voids) and thus the coordination number of calcium ions is eight. Other substances which exist in this kind of structure are UO2, and ThO2. 


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