 |  |  | |
| CsCl | NaCl | ZnS | |
| description | cubic Cl– with Cs+ in all cubic sites | face-centred cubic Cl– with Na+ in all octahedral sites | face-centred cubic S2– with Zn2+ in half of the tetrahedral sites |
| coordination number: | Cs+ = Cl– = 8 | Na+ = Cl– = 6 | Zn2+ = S2– = 4 |
| ionic radii/pm | Cs+ = 170; Cl– = 181 | Na+ = 102; Cl– = 181 | Zn2+ = 84; S2– = 184 |
The coordination number of the ion occupying the sites is obvious from the description because it equals the number of ions involved in the site. If the anion and cation are present in equal number, their coordination number is the same.
Sites with fewer ions around them are smaller. Site size also depends on the size of the ions surrounding the site. For these solids the ion sizes are very similar. Note that the smallest cation (Zn2+) occupies the smallest site and has the lowest coordination number.