CaO has a face-centered cubic unit cell in which the O2- anions occupy corners and face centers, while the cations fit into the hole between adjacent anions. What is its density if the ionic radii of Ca2+, O2- ions are 57.63 pm and 184.0 pm, respectively?

To find the density of CaO, we need to determine the volume of the unit cell and the total mass of the unit cell.

1. Start by finding the length of the unit cell (a):
- In a face-centered cubic lattice, the length of the unit cell (a) is related to the radius of the anions (O2-) by the formula:
a = 4 * r_O
- Substitute the ionic radius of O2- (r_O = 184.0 pm) into the formula to find the length of the unit cell.

2. Calculate the volume of the unit cell:
- In a face-centered cubic lattice, the volume of the unit cell (V) is given by the formula:
V = a^3
- Substitute the value of a (obtained in step 1) into the formula to calculate the volume.

3. Determine the total number of atoms in the unit cell:
- In a face-centered cubic lattice, there are 4 atoms per unit cell (1 Ca2+ and 2 O2-).
- Multiply the volume of the unit cell (V, obtained in step 2) by the number of atoms per unit cell to calculate the total volume occupied by the atoms in the unit cell.

4. Calculate the mass of the unit cell:
- Determine the molar mass of CaO by summing the atomic masses of Ca and O.
- Multiply the molar mass by the number of moles of CaO in the unit cell (which is equal to the number of atoms, obtained in step 3) to get the total mass of the unit cell.

5. Calculate the density:
- Divide the mass of the unit cell (obtained in step 4) by the volume occupied by the atoms in the unit cell (obtained in step 3) to calculate the density.

(Note: Remember to convert the units as necessary during the calculations.)

By following these steps, you should be able to find the density of CaO.