Question

Specify the co-ordination number of Calcium and Fluoride ion in the compound Calcium fluoride ${\mathrm{CaF}}_2$

Answer 1

Coordination number:

1. The total number of spheres or particles nearest to the other particles in the crystal lattice is known as the coordination number of compounds.
2. Calcium fluoride is made up of two anions of fluorine ion ${\mathrm{F}}^{-}$ and a cation of calcium ion ${\mathrm{Ca}}^{2+}$. They combine to generate a compound formula ${\mathrm{AB}}_2$.
3. Calcium ions ${\mathrm{Ca}}^{2+}$ have a tendency to form cubic close packing in calcium fluoride compounds. Calcium ions ${\mathrm{Ca}}^{2+}$ are surrounded by eight atoms of fluorine ion ${\mathrm{F}}^{-}$ in this arrangement.
4. In the Calcium fluoride compound, the fluorine ion ${\mathrm{F}}^{-}$ is organized in a tetrahedral structure, occupying all of the tetrahedron's apices. As a result, each Fluorine atom is surrounded by four ${\mathrm{Ca}}^{2+}$ ions.

Therefore, the coordination number of calcium is $8$, and that of fluorine is $4$.