Question

In $Ca{F}_2$ unit cell the co ordination number of $F^{-}$ ion is?

Answer 1

Simple ionic structures are described by two coordination numbers, one for each type of ion.

Calcium fluoride $\left(Ca{F}_2\right)$ is an (8, 4) structure,

each cation $C{a}^{2+}$is surrounded by eight $F^{-}$ anion neighbors,

each anion $F^{-}$ by four $C{a}^{2+}$.

So coordination number of $C{a}^{+2}=8$ and $F^{-}=4$ ion in $Ca{F}_2$ crystal