A compound forms hexagonal close-packed structure. What is the total number of voids in 0.5 mol of it? How many of these are tetrahedral voids?

Number of atoms in close packing = 0.5 mol

1 mol has 6.022x1023 particles

So that  

Number of close- packed particles = 0.5 × 6.022 × 1023   = 3.011 × 1023    

Number of tetrahedral voids = 2 × number of atoms in close packing plug the value we get

Number of tetrahedral voids = 2 × 3.011 × 10 23  = 6.022 × 10 23  

Number of octahedral = number of atoms in close packing 

So that 

Number of octahedral voids = 3.011 × 10 23 

Total number of voids = tetrahedral voids + octahedral voids

;       = 6.022 × 10 23 + 3.011 × 10 23  

;       = 9.03 × 10 23