The s-Block Elements

BeO is covalent in nature due to its smaller size, high ionisation enthalpy and high electronegativity and therefore it is insoluble in water. On the order hand, BeSO₄ is ionic. Also because of small size of Be²⁺ ion, the hydration enthalpy of BeSO₄ is much higher than its lattice enthalpy. Thus BeSO₄ is highly soluble in water.

BaO and BaSO₄ are ionic compounds. Further the size of O^2– ion is much smaller as compared to that of SO₄^2– ion. Also, a bigger anion stabilises a bigger cation more than a smaller anion stabilises a bigger cation. As a result lattice enthalpy of BaO is much less than that of BaSO₄ and hence BaO is insoluble in water while BaSO₄ is soluble.

BaO and BaSO₄ are ionic compounds. Further the size of O^2– ion is much smaller as compared to that of SO₄^2– ion. Also, a bigger anion stabilises a bigger cation more than a smaller anion stabilises a bigger cation. As a result lattice enthalpy of BaO is much less than that of BaSO₄ and hence BaO is insoluble in water while BaSO₄ is soluble

BeCl₂ reacts with moisture to form HCl while other halides do not.