Ionic Bonding

The alkaline earth oxides MgO and BaO adopt the rock salt (NaCl) structure with cell parameters a of 4.213 à… and 5.139 à…. Using 1.40 à… as the radius for the oxide ion:

a) Calculate the radius ratios r(M2+) / r(O2-) for these compounds

b) Using the radius ratio rule, indicate whether or not the value found are in agreement with the
adoption of the NaCl structure by these compounds. Justify your answer.