<P> When ionic compounds dissolve, the individual ions dissociate and are solvated by the solvent and dispersed throughout the resulting solution . Because the ions are released into solution when dissolved, and can conduct charge, soluble ionic compounds are the most common class of strong electrolytes, and their solutions have a high electrical conductivity . </P> <P> The solubility is highest in polar solvents (such as water) or ionic liquids, but tends to be low in nonpolar solvents (such as petrol / gasoline). This is principally because the resulting ion--dipole interactions are significantly stronger than ion - induced dipole interactions, so the heat of solution is higher . When the oppositely charged ions in the solid ionic lattice are surrounded by the opposite pole of a polar molecule, the solid ions are pulled out of the lattice and into the liquid . If the solvation energy exceeds the lattice energy, the negative net enthalpy change of solution provides a thermodynamic drive to remove ions from their positions in the crystal and dissolve in the liquid . In addition, the entropy change of solution is usually positive for most solid solutes like ionic compounds, which means that their solubility increases when the temperature increases . There are some unusual ionic compounds such as cerium (III) sulfate, where this entropy change is negative, due to extra order induced in the water upon solution, and the solubility decreases with temperature . </P> <P> Although ionic compounds contain charged atoms or clusters, these materials do not typically conduct electricity to any significant extent when the substance is solid . In order to conduct, the charged particles must be mobile rather than stationary in a crystal lattice . This is achieved to some degree at high temperatures when the defect concentration increases the ionic mobility and solid state ionic conductivity is observed . When the ionic compounds are dissolved in a liquid or are melted into a liquid, they can conduct electricity because the ions become completely mobile . This conductivity gain upon dissolving or melting is sometimes used as a defining characteristic of ionic compounds . </P> <P> In some unusual ionic compounds: fast ion conductors, and ionic glasses, one or more of the ionic components has a significant mobility, allowing conductivity even while the material as a whole remains solid . This is often highly temperature dependant, and may be the result of either a phase change or a high defect concentration . These materials are used in all solid - state supercapacitors, batteries, and fuel cells, and in various kinds of chemical sensors . </P>

How lattice energy control the solubility of ionic compound