Question

A fluorite ($Ca{F}_2$) structure can be described as a simple cubic lattice of cations with anions in the alternate cubic void. The number of cations present in a unit cell is_________.

Answer 1

From the structure given below, it can be seen that every unit cell contains $4C{a}^{+2}$ ions.

To see that each cation is in a cubic void formed by anions, we can extend the lattice and see that each cation is surrounded by $8$ anions.