Question

A cubic unit cell contains manganese ions at the corners and fluoride ions at the centre of each edge.

(a) What is the empirical formula of the compound?

(b) What is the coordination number of the $Mn$ ion?

• A. $Mn{F}_3,$ $4$
• B. $Mn{F}_3,$ $6$
• C. $M{n}_2{F}_3,$ $4$
• D. $M{n}_2{F}_3,$ $6$

Answer 1

The correct option is B $Mn{F}_3,$ $6$

Number of Manganese ions per unit cell $=\frac{1}{8}\times 8=1$
Number of flouride ions per unit cell $=\frac{1}{4}\times 12=3$
Hence the empirical formula becomes $Mn{F}_3$
Each corner is connected by 6 edges, therefore the coordination number of $Mn$ atoms at the corners is 6.