Question

In calcium fluoride, having the fluorite structure the coordination numbers for the calcium ion $C{a}^{2+}$ and fluoride ion $\left(F^{-}\right)$ are

• A. 4 and 2
• B. 6 and 6
• C. 8 and 4
• D. 4 and 8

Answer 1

The correct option is C

8 and 4

$Ca{F}_2\to A{B}_2$ type structure (Fluorite type)
$C{a}^{2+}\to$ Face central cubic lattice points
$F^{-}\to$ tetrahedral voids
Each $C{a}^{2+}$ surrounded by $8F^{-}$ ions
Each $F^{-}$ surrounded by $4C{a}^{2+}$ ions
C.N. of $C{a}^{2+}$ and $F^{-}$ are 8 and 4 respectively