Substances that dissociate completely into ions when placed in water are referred to as
strong electrolytes because the high ionic concentration allows an electric current to pass through the solution. Most compounds with ionic bonds behave in this manner; sodium chloride is an example.
By contrast, other substances—like the simple sugar glucose—do not dissociate at all and exist in solution as molecules held together by strong covalent bonds. There also are substances—like sodium carbonate (Na 2CO 3)—that contain both ionic and covalent bonds. (See Figure 1.)
Figure 1. Ionic and covalent bonding in Na2CO3.