Calcium sulfide has a face-centered cubic unit cell with calcium ions in octahedral holes and sulfide ions at the lattice points. How many ions of each element are contained in each unit cell

4 calcium ions and 4 sulfide ions.

Explanation:

In a face centered unit cell, 8 corners of the unit cell are occupied by 8 atoms. Each corner is 1/8 of a cell. In addition it has 6 atoms in the face of the lattice, which is 1/2 of a cell. (1/8 * 8) + (1/2 * 6) = 4. CaS has a 1:1 ratio. Therefore, they each have 4 ions.

"the periodic table is arranged in order of atomic number."

c (diamond),

sio2 (quartz)