# Question #73c28

Dec 22, 2017

1 Cl ion per unit cell
1 Cs ion per unit cell
A total of 2 ions per unit cell

#### Explanation:

CsCl has a primitive cubic structure, shown below:

At first glance, you may think that this is a body-centered structure. But, the ion in the center (Cs) is different to the surrounding ions (Cl).

To work out the number of ions per unit cell, you cannot just count them, as the ions are shared with the surrounding unit cells.

The Cs is in the center of the unit cell, and is not shared so there is 1 Cs ion per unit cell.

The Cl ions are on the corners, thus are shared with 8 other unit cells.

$\frac{1}{8} \times 8 = 1$ Cl ion per unit cell

Therefore, you have:

1 Cl ion per unit cell
1 Cs ion per unit cell
A total of 2 ions per unit cell