Question

Predict the coordination number of Ca2+ in CaO crystal and also its crystal
structure. [Hint: use data for ionic radii values given in your Unit]​

Answer 1

On the basis of ionic charge and ionic radii given in Table 12.3, predict crystal structures for the following materials:

(a) CaO

(b) MnS

(c) KBr

(d) CsBr

Justify your selections.

Table 12.3 Ionic Radii for Several Cations and Anions for a Coordination Number of 6

Cation

Ionic Radius (nm)

Anion

Ionic Radius (nm)

Al3+

0.053

Br–

0.196

Ba2+

0.136

Cl–

0.181

Ca2+

0.100

F–

0.133

Cs+

0.170

I–

0.220

Fe2+

0.077

O2-

0.140

Fe3+

0.069

S2-

0.184

K+

0.138

Mg2+

0.072

Mn2+

0.067

Na+

0.102

Ni2+

0.069

Si4+

0.040

Ti4+

0.061

Step-by-step solution:

Step 1 of 3

(a)

Obtain the atomic radii of calcium and oxygen from Table 12.3.

Atomic radius of calcium,

Atomic radius of oxygen,

Calculate the ratio of atomic radius of calcium and atomic radius of oxygen.

Obtain the coordination number for each cation from Table 12.2.

Predict the crystal structure from Table 12.4 for the given coordination number. And the crystal structure is sodium chloride.

Therefore, the crystal structure of CaO is structure