Secondary Interactions and Determining Structure and Properties Of Matter - Session 2

Ion Induced Dipole Interaction.An ion is a molecule or atom which has a charge. An induced dipole occurs when an ion or dipole induces a dipole in another atom or molecule which had no dipole. These are weak forces. So, the interaction between an ion, and an induced dipole, is called an ion-induced dipole interaction. It is a weak attraction. This happens when the approach of an ion induces a dipole in an atom or molecule which is non-polar by disturbing its arrangement of electrons.

What happens when I₂ is dissolved in aqueous KI.I₂ is a non-polar molecule. When I₂ reacts with the KI solution it makes KI₃. KI₃ is an ionic compound. So in the presence of aqueous KI, the iodine molecule becomes polar by the formation of KI₃.

Dipole-induced dipole.A dipole-induced dipole interaction is a weak attraction. This results when polar molecules approach non-polar molecules and induces dipole in them by disturbing the arrangement of electrons. Negative part of polar molecule repels the negative charges in non polar molecule. In this way non polar molecule becomes slightly polar or a dipole is induced in it. So a weak interaction develops between both molecules. This weak interaction is called dipole induced dipole interaction.

Oxygen dissolved in water. Oxygen is dissolved in water by direct diffusion and surface water agitation. Oxygen solubility in water is so small and it takes a lot of time for oxygen to dissolve in water. As Oxygen is a non-polar molecule and water is polar it has very low solubility. But Oxygen is dissolved in water by dipole-induced dipole interaction.I₂ dissolved in water.I₂ is a non-polar molecule. It cannot dissolve in polar water molecules directly but it can be dissolved first in an aqueous KI solution and become a polar ionic compound in KI₃ form. After that, it can be dissolved in water.

Xenon is the most soluble gas in water. It is due to dipole-induced dipole interaction between Xe and water molecules. The dipole-induced dipole interaction becomes stronger with the increment of molecular mass of noble gases. Therefore its solubility improves downwards the group making xenon the most soluble gas in water.

London forces.London forces is a temporary attractive force that results when electrons in two adjacent atoms take up a position that makes atoms form temporary dipoles. This is why it is sometimes called induced-dipole induced-dipole attraction. These are intermolecular forces of attraction that hold molecules together. It is a weak force resulting from the motion of electrons that creates temporary dipoles in molecules.

Fluoromethane.The Methyl group is an electro-positive group that is attached to an atom of the highly electronegative element fluorine. This electronegativity between the methyl group and fluorine atoms results in permanent dipoles. Therefore dipole dipoles' attractive forces exist between CH₃F molecules.

Carbon Tetrachloride.CCl₄ has London dispersion forces as intermolecular forces, which keep its molecule together. although Cl-Cl bonds are polar there is no dipole-dipole moment in the CCl₄ molecule. the polar effect of CCl get canceled out by its opposite C-Cl, so the overall dipole moment is zero. Therefore, London dispersion forces hold the molecules together.