(ii) All alkaline earth metals react with `O_(2)` to form their respective oxides (MO) , their reactivity , however , increases down the group with increase in atomic size .
Solubility in water . BeO being covalent is insoluble in water , MgO is only sparingly soluble in wate but all other oxides , i.e. , CaO , SrO and BaO dissolve in water with evolution of heat forming their corresponding hydroxides .
`CaO + H_(2)O to Ca(OH)_(2) + ` heat
The solubility of these oxides/hydration increase down the group because both the their lattice enthalpies and hydration enthalpies decrease down the group but their lattice enthalpies decrease more rapidly than their hydration enthalpies .
Nature of oxides . Due to small size and somewhat high ionization enthalpy of Be, BeO is amphoteric and dissolves in both acids and alkalies .
`BeO + 2HCl to BeCl_(2) + H_(2)O , BeO + 2 NaOH to underset("Sodium berrylate")(Na_(2)BeO_(2)) + H_(2)O`
All other oxides are basic in nature and their basic character increases down the group .