Ionic crystals

Question 1

What coordination is NaCl?

Answer 1

6:6

Question 2

What coordination is CsCl?

Answer 2

8:8

Question 3

What coordination is ZnS?

Answer 3

4:4

Question 4

Why is NaCl 6:6 coordination?

Answer 4

Na+ touches 6 Cl- atoms
Cl- touches 6 Na+ atoms
because they fill the octahedral holes of the layers. It is FCC.

Question 5

Why is CsCl 8:8 coordination?

Answer 5

Cs+ touches 8 Cl- atoms
Cl- touches 8 Cs+ atoms
Its not CCP

Question 6

What is the radius ratio?

Answer 6

R+/R-

Question 7

What is a limiting radius ratio?

Answer 7

The minimum allowable value for the ratio of ionic radii for this structure to be stable.

Question 8

What is the the effect of a smaller cation on a molecule’s stability?

Answer 8

A smaller cation can increase the stability of a molecule because the distance between cation and anions decreases and the energy of the system decreases meaning its more stable.

Question 9

What is the limiting radius ratio for 8:8 coordination (CsCl structure)?

Answer 9

> 0.73

Question 10

What is the limiting radius ratio for 6:6 coordination (NaCl structure)?

Answer 10

> 0.41

Question 11

What is the limiting radius ratio for 4:4 coordination (ZnS structure)?

Answer 11

<0.41, >0.23

Question 12

What is the coordination of CaF2 (fluorite structure)?

Answer 12

8:4 because:
each Ca2+ touches 8 F-
each F- touches 4 Ca2+

Question 13

What is an example of 6:3 coordination?

Answer 13

TiO2 (rutile)

Question 14

What is an example of 4:2 coordination?

Answer 14

SiO2 (Quartz)