The second ionisation enthalpy of Mg is sufficiently high while the second electron affinity or electron gain enthalpy of oxygen is low (actually this value is positive), yet Mg^(2+) and O^(2-) ions form ionic compound, MgO. Explain with reasons.

The second ionisation enthalpy of Mg is sufficiently high while the se

1.	The second ionisation enthalpy of Mg is sufficiently high while the second electron affinity or electron gain enthalpy of oxygen is low (actually this value is positive), yet Mg^(2+) and O^(2-) ions form ionic compound, MgO. Explain with reasons.
Answer» Solution :The sufficiently high second ionisation enthalpy of Mg indicates that a large amount of ENERGY is required to remove second electron from the Mg-atom. i.e, to CONVERT `Mg^(+)` to `Mg^(2+)` ion. The second electron gain enthalpy of oxygenn is positive indicating that the energy should be supplied to convert O-atom into `O^(2-)` ion. since, both the processes are endothermic, MGO is not expected to be produced through the formation of ionic bond. but actually, it is produced and this is because of its high lattice energy (mainly due to comparable sizes of `Mg^(2+) and O^(2-)` IONS.)