Why are some covalent compounds soluble in water and others are not?
A net dipole moment exists within the water molecule due to the strong electronegativity of oxygen, hence, the area near the oxygen is partially negative while the area near the hydrogen is partially positive; it is polar. This causes strong hydrogen bonds with each water molecule (positive interacts with the negative). Water solubility occurs when a species successfully interacts with the water molecule by interrupting these hydrogen bonds. Thus, if a covalent compound also has a considerable net dipole moment or polar, it could dissolve in water. Presence of an electronegative element in an unsymmetrical molecule may do the thing. However, if a compound does not have an electronegative element or is symmetrical, it cannot break the self-interaction of water molecules and therefore, not dissolve.
