This study reports how instruction including visualization strategies associated with computer animations and electron density plots affected students' conceptual understanding of two chemistry topics. Two sets of students responded to several conceptual questions about molecular polarities and miscibilities and these responses were compared. One group received instruction including the use of wooden model kits and physical demonstrations; the other received similar instruction with the additional use of computer animations and electron-density plots. Students who viewed electron-density plots were more likely to identify symmetric molecules with polar bonds as being nonpolar and provided more complete descriptions of how soap molecules help remove grease from an object. Students who viewed computer animations and electron density plots were also more likely to explain that the intermolecular attractions among water molecules are responsible for the immiscibility of oil and water, and were more likely to recognize that water molecules are attracted to each other and to sodium and chloride ions but are not strongly attracted to hydrogen molecules. Although other studies have shown that computer animations can improve students' conceptual understanding of chemistry, this is the first to demonstrate that electron-density plots mapped with electrostatic potentials can also be an effective visualization strategy.