Question

The co-ordination number of cation and anion in $Ca{F}_2$ and $CsCl$ are respectively.

• A. $8:4$ and $6:3$
• B. $6:3$ and $4:4$
• C. $8:4$ and $8:8$
• D. $4:2$ and $2:4$

Answer 1

The correct option is A $8:4$ and $6:3$

The co-ordination number of cation and anion in $Ca{F}_2$ and $CsCl$ are 8:4 and 8:8 respectively.
In $Ca{F}_2$ unit cell, $C{a}^{2+}$ ions form fcc unit cell and $F^{-}$ ions are present in tetrahedral voids. Each $C{a}^{2+}$ ion is surrounded by 8 $F^{-}$ ions. Each $F^{-}$ ion is surrounded by 4 $C{a}^{2+}$ ions.
In $CsCl$ unit cell, $C{l}^{-}$ ions are present at corners of cube and $C{s}^{+}$ ions are present at body center which is a cubic void. Each $C{l}^{-}$ ion is surrounded by 8 $N{a}^{+}$ ions.
Each $N{a}^{+}$ ion is surrounded by 8 $C{l}^{-}$ ions.