Question

In calcium fluoride having the fluoride structure, the coordination numbers for calcium ion $\left( {C{a^{2 + }}} \right)$ and fluoride ion $\left( {{F^ - }} \right)$ are:
A.$8$ and $4$
B.$4$and $8$
C.$4$ and $2$
D.$6$ and $6$

Answer 1

Calcium fluoride crystallises in a face centred cubic unit cell. Fluoride ions have four neighbours of the opposite charges arranged at the tetrahedron and not only this but the calcium cations have eight neighbours arranged at the corner that further outlines the smaller cube.

Complete step by step answer:
Firstly we will discuss the meaning of the word coordination number so it is basically the number of bonds the central metal atom is bonded to.
Here we will look at how we will write the chemical formula of the calcium fluoride. So it is written as $Ca{F_2}$. Further we will talk about the number of ions in each calcium and fluoride.so the fluoride can be written as ${F^ - }$ and further the calcium can be written as $C{a^{2 + }}$. As they are found to contain the different ions therefore they will definitely have the different coordination number. Moreover talking on this we come to know that calcium fluoride crystallises in a face centred cubic unit cell. Further it has an edge length that is calculated to be as $5.463$ angstroms.moreover talking on it we will find that that the calcium ions defines the FCC sites and further the fluoride ions occupy all the tetrahedral sites. Moving on the concept in little more detail we come to know that the fluoride ions have four neighbours of the opposite charges arranged at the tetrahedron and not only this but the calcium cations have eight neighbours arranged at thee corner that further outlines the smaller cube. So the coordination number of calcium ion and fluoride ion is $8:4$.
Hence from this we concluded that the correct option is A.

Note:
We should here note that the calcium fluoride is used for the production of various chemical compounds.it is interesting to note here that the calcium fluoride is used for the manufacture of the optical components.