Ion-Dipole Interactions (College Board AP® Chemistry): Revision Note

Ion-Dipole Interactions

• Ion-dipole forces act between an ion and a polar molecule

• They account for the dissolving of ionic compounds in polar solvents such as water

• For example, in a solution of sodium chloride, NaCl, in water:

  • The oxygen atom has a partial negative (δ^-) charge

  • The hydrogen atoms have a partial positive charge (δ⁺)

  • Overall, there is a dipole moment within the water molecule

    • The Na⁺ ion is attracted to the negative end of the dipole

    • The Cl^- ion is attracted to the positive end of the dipole

Water molecules around sodium and chloride ions

Ion-dipole interaction between sodium and chloride ions with water

• The magnitude of ion-dipole interactions increases as either the ionic charge or the magnitude of the dipole moment increases

• Ion-dipole forces tend to be stronger than dipole-dipole forces