solubility

• For a substance to dissolve, bonds within the solute and solvent must break and bonds between the solute and solvent must form.

• In general, a substance will not dissolve if the bonds to be broken are stronger than the bonds that will be formed.

Polar and non-polar solvents

• Most ionic substances will dissolve in polar solvents, because the ion-dipole bonds formed are strong enough.

• Most ionic substances will not dissolve in non-polar solvents, because the bonds between the ions are too strong for the non-polar molecules to pull them away from the ionic lattice.

• Most covalent molecules will dissolve in non-polar solvents, because the intermolecular bonds between covalent molecules are usually weak so can be broken by the non-polar solvent molecules.

• Most covalent molecules will not dissolve in polar solvents, because the intermolecular bonds between polar solvent molecules are too strong.

Aqueous solution

• Ion-dipole bonds form between ions and water molecules when an ionic substances is dissolved in water.

• The δ+ hydrogens are electrostatically attracted to the negative ions.

• The δ- oxygens are electrostatically attracted to the positive ions.

• When an ionic substance dissolves in water, the ions separate from the ionic lattice and become surrounded by water molecules. This is called hydration and the ions are described as hydrated.

• If the solvent is not water, this process is called solvation instead.