Learning Objective: To learn about the factors affecting ion-dipole interaction strength.
Skill Level - Intermediate
Prerequisites:
Chapter: Intermolecular Forces
Sub-topic: Ion-Dipole Interactions
Author's Note: The magnitude of ion-dipole interaction depends on the sizes of the ions and the solvent polarity. This section teaches how to judge the strength of the interaction based on the size of the ion, ionic charge, and the related enthalpy of hydration values by offering plenty of examples. We also learn that it's not only the solvent polarity that is important for ion-dipole interaction but also a factor known as the dielectric constant since we don't want the oppositely charged ions to combine again but remain separated for maximum ion-solvent interaction and dissolution.
Factor Affecting the Ion - Dipole Strength
As ion-dipole forces are attractive electrostatic interactions, the strength of the ion-dipole interaction depends on – the size and charge of the ion and the magnitude of the dipole in the polar molecule.
1) Charge and size of the ions
A neutral atom always has equal nuclear protons and outer nuclear electrons. Once an atom loses an electron, the proton in its nucleus exceeds the number of electrons. This excess number of protons (or the number of lost electrons) is denoted by a number and a positive charge, and the species is known as a cation.
For example, the Na atom with 11 protons and 11 electrons is neutral. On losing an electron, it now has 11 protons and 10 electrons; the excess of the proton is denoted as Na+.
The loss of an electron also causes the nucleus to hold its remaining outermost electrons firmly. This attractive inward pull from the nucleus also shrinks the ion's size. The higher the loss of electrons, the smaller the size of the cation.
The smaller-sized cations with greater charges have.....
For example, between the Na+ and Mg2+....
Also, if you compare the sizes of both cations and anions...
An increase in the size of an ion down the group...
Since the anion is common in both (SO4-2), the difference is due to the....
2) Magnitude of the Dipole and dielectric constant
Solvent polarity determines how well an ionic compound interacts with the solvent. Such a polarity in the molecule results from the electronegativity difference between the combining atoms.
The higher the electronegativity difference between....
However, for the ions to stay separated....
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