Ion Exchange

Ions are electrically charged atoms or groups of atoms. Ion exchange is the phenomenon of replacing one ion with another of similar charge. Ion exchange resins are solids containing strongly bonded charged atom groups. (Positively charged atoms are called cations; negatively charged, anions.) They occur as natural materials and can Invertebrates make up 97% of the animal kingdom, the largest of the five kingdoms of living organisms. Illustration by Hans & Cassidy. Courtesy of Gale Group. be synthetically made. An ion of opposite charge is loosely bound to a charged group. When placed in contact with an ionic solution (a solution of an ionic substance), the loosely bound ions are replaced by those in solution and are retained on the solid. Ion exchange membranes are sheet-like films which allow the passage of ions while restricting the crossing of larger, uncharged molecules.