Why does calcium oxide and sodium chloride have different melting points?

CaO has a double bond since there is a transfer of two electrons from the calcium to the oxygen. NaCl only has a single bond. Also, the EN difference between Ca and O is greater compared to that of Na and Cl. This means there is a greater dipole-dipole force (polarity) present. Basically, it has a stronger attraction between its cations and anions.