Weblink 6.1 Common structures adopted by ionic crystals

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• In the NaCl structure, six sodium ions (shown in blue) are each surrounded by six chloride ions (shown in green). The coordination is therefore 6:6
• In the CsCl structure, the caesium ion (green) is surrounded by eight chloride ions (blue). Although it is not obvious from this fragment of the structure shown here, each chloride is also surrounded by eight caesiums, making the coordination 8:8
  
• In the wurtzite (ZnS) structure, each zinc ion (blue) is surrounded by four sulfide ions (yellow). In the same way, each sulfide is surrounded by four zincs, making the coordination 4:4
  
• In the fluorite (CaF₂) structure, each fluoride ion (green) is surrounded by four calcium ions (blue), and each calcium by eight fluorides. The coordination is therefore 4:8