NaCl and CsCl have similar formular . Then why they have differnet strutures ?

Explanation

The radius ratio of NaCl `(r_(Na^+)//r_(Cl^-))` lies in the range 0.414 -0.732. Hence , it has a coordination number of 6, i.e., octahedral arrangement . On the other hand, the radius ratio of CsCl `(r_(Cs^+)//r_(Cl^-))` lies in the range 0.732-1.0 . Hence, it has a coordination number of 8, i.e., it has a body-centred cubic arrangement.