When we dissolve a solute into a solvent, there's an interplay between forces. Relatively strong solvent-solute interactions promote the process of dissolving. These interactions must overcome the solute-solute interactions and solvent-solvent interactions. This is why we say, "like dissolves like." For example, when we dissolve the ionic solid sodium chloride into water, the interactions between the water molecules and the ions should be very strong compared to the interactions between the sodium and chloride ions or between two water molecules. As a polar solvent, water has a partial positive and a partial negative. The partial negative is attracted to the sodium cations; the partial positive is attracted to the chloride anions. This is why polar solvents are generally useful for dissolving ionic compounds. In the process of dissolving, the cumulative effect of the water molecules being attracted to the ion allows the water molecules to remove the ion from the crystal lattice. In solution, we see each cation is surrounded by the partial negative side of multiple water molecules and each anion is surrounded by the partial positive of many water molecules. Soluble ionic compounds are strong electrolytes, producing cations and anions when dissolved in solution. A strong electrolyte can carry a current in solution by producing many ions when it's dissolved. The cations are attracted to the negative terminal and the anions are attracted to the positive terminal. This movement of ions carries the current in solution. Strong acids are also strong electrolytes because they break up completely to form ions in solution, which are able to carry the current. Weak electrolytes are only weak conductors of electricity in solution. A weak acid is an example of a weak electrolyte; acetic acid is a weak acid and it only ionizes to a very small extent. Usually less than 5% of the molecules produce ions, while most of the molecules stay together in solution. Nonelectrolytes may dissolve in solution, but they do not form ions so they cannot carry current. When we dissolve sugar in water, there are relatively strong attractions between the sugar molecules and water, so sugar is able to dissolve. However, the sugar molecules are left intact when they dissolve: they do not produce ions.