<Tr> <Th> </Th> <Th> </Th> <Th> occupancy </Th> <Th> critical radius ratio </Th> <Th> name </Th> <Th> Madelung constant </Th> <Th> name </Th> <Th> Madelung constant </Th> </Tr> <Tr> <Td> MX </Td> <Td> 6: 6 </Td> <Td> all octahedral </Td> <Td> 0.4142 </Td> <Td> sodium chloride </Td> <Td> 1.747565 </Td> <Td> nickeline </Td> <Td> <1.73 </Td> </Tr> <Tr> <Td> </Td> <Td> 4: 4 </Td> <Td> alternate tetrahedral </Td> <Td> 0.2247 </Td> <Td> zinc blende </Td> <Td> 1.6381 </Td> <Td> wurtzite </Td> <Td> 1.641 </Td> </Tr> <Tr> <Td> MX </Td> <Td> 8: 4 </Td> <Td> all tetrahedral </Td> <Td> 0.2247 </Td> <Td> fluorite </Td> <Td> 5.03878 </Td> <Td> </Td> <Td> </Td> </Tr>

Describe in general terms the structure of ionic solids such as nacl