Exercise 7 | Liquids and Solids
Crystalline potassium fluoride has a face-centered cubic array of anions with an interpenetrating face-centered cubic cation lattice.
How many potassium ions and fluoride ions are there per unit cell?
Face-centered cubic lattice:
- 1 atom at the corner ( x 8 corners)
- 3 atoms at the center of each face ( x 6 faces)
⇒ 4 anions
⇒ 4 fluoride ions
Same for cations:
⇒ 4 cations
⇒ 4 potassium ions
(We know also that potassium fluoride is neutral ⇒ same number of fluoride ions and potassium ions)