Why MgO is insoluble in water?

MgO (magnesium oxide) is insoluble in water due to its strong ionic bonding.

MgO is composed of magnesium cations (Mg2+) and oxide anions (O2-). In the solid state, these ions are held together by strong electrostatic forces of attraction. The magnesium cations are attracted to the oxide anions, forming a lattice structure.

When MgO is added to water, the water molecules are highly polar, with a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. These polar water molecules are attracted to the ions in MgO.

However, the attraction between the water molecules and the ions in MgO is not strong enough to overcome the strong ionic bonding within the solid. The electrostatic forces holding the magnesium cations and oxide anions together are much stronger than the forces of attraction between the water molecules and the ions.

As a result, MgO remains intact as a solid and does not dissociate into individual ions in water. This lack of dissociation prevents MgO from dissolving in water, making it insoluble.