Ion-Dipole Force



 

Learning Objective

  • Define ion-dipole force.

Key Points

    • An ion-dipole interaction occurs between a fully charged ion and a partially charged dipole.
    • The strength of the ion-dipole force is proportionate to ion charge.
    • An ion-induced dipole interaction occurs between a fully charged ion and a temporarily charged dipole. The temporary dipole is induced by the presence of the ion.

Terms

  • ion-dipole forcesAn electrostatic interaction involving a permanent dipole in one molecule and an ion.
  • ionAn atom or group of atoms bearing an electrical charge, such as sodium and chlorine in table salt.
  • ion-induced dipole forceAn electrostatic interaction involving a temporary dipole in one molecule and a permanently charged ion.

Ion-Dipole Force

Ion-dipole and ion-induced dipole forces operate much like dipole-dipole and induced dipole-dipole interactions. However, ion-dipole forces involve ions instead of solely polar molecules. Ion-dipole forces are stronger than dipole interactions because the charge of any ion is much greater than the charge of a dipole; the strength of the ion-dipole force is proportionate to ion charge. Ion-dipole bonding is also stronger than hydrogen bonding. An ion-dipole force consists of an ion and a polar molecule aligning so that the positive and negative charges are next to one another, allowing for maximum attraction.

Ion-dipole forcesIon-dipole forces are generated between polar water molecules and a sodium ion. The oxygen atom in the water molecule has a slight negative charge and is attracted to the positive sodium ion. These intermolecular ion-dipole forces are much weaker than covalent or ionic bonds.

Ion-Induced Dipole Force

An ion-induced dipole force occurs when an ion interacts with a non-polar molecule. Like a dipole-induced dipole force, the charge of the ion causes a distortion of the electron cloud in the non-polar molecule, causing a temporary partial charge. The temporary partially charged dipole and the ion are attracted to each other and form a fleeting interaction.