Question

b) Predict the coordination number of Ca2+ in CaO crystal and also its crystal

structure. ​

Answer 1

coordination number of Ca2+ in CaO will be 6.

Though I don't know about second part.

Answer 2

Radius ratio rule is applied to find out the coordination number of the Ca2+ ion in CaO.

Here, radius of Ca2+ ion = 100pm and Radius of O2- ion = 145pm (approximately)

r+/r- = 100/145 = 0.6896.

Now, this number is in the range of 0.414 < 0.6896 < 0.732

Hence, the coordination number of Ca2+ ion in CaO is 6.

The structure of the CaO molecule is similar to NaCl where the arrangement of face-centred cubic of the O2- ion with the interpenetrating face-centred cubic lattice of Ca2+ ions.