2.8.4

Ion-Dipole Interactions

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Ion-Dipole Interactions

The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.

Dissociation

Dissociation

  • When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution.
  • This is because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them.
    • This process represents a physical change known as dissociation.
Ionic compounds & dissociation

Ionic compounds & dissociation

  • Under most conditions, ionic compounds will dissociate nearly completely when dissolved, and so they are classified as strong electrolytes.
  • Even sparingly, soluble ionic compounds are strong electrolytes, since the small amount that does dissolve will dissociate completely.
Dissolving KCl

Dissolving KCl

  • Consider what happens at the microscopic level when solid KCl is added to water.
    • Ion-dipole forces attract the positive (hydrogen) end of the polar water molecules to the negative chloride ions at the surface of the solid.
    • The ion-dipole forces also attract the negative (oxygen) ends to the positive potassium ions.
Dissolving KCl - 2

Dissolving KCl - 2

  • The water molecules surround individual K+ and Cl- ions.
  • This reduces the strong interionic forces that bind the ions together and letting them move off into solution as solvated ions.
  • Overcoming the electrostatic attraction permits the independent motion of each hydrated ion in a dilute solution.
    • Eventually the ions transition from fixed positions in the undissolved compound to widely dispersed, solvated ions in solution.
Diagram
Strength

Strength

  • Ion-dipole reactions tend to be stronger than dipole-dipole interactions, but weaker than hydrogen bonds.
  • The greater the charge of the ion, the strong the ion-dipole interaction will be.
Jump to other topics
1

Structure - Models of the Particulate of Matter

2

Structure - Models of Bonding & Structure

3

Structure - Classification of Matter

3.1

The Periodic Table: Classification of Elements

3.2

Periodic Trends

3.3

Group 1 Alkali Metals

3.4

Halogens

3.5

Noble gases, group 18

3.6

Functional Groups: Classification of Organic

3.7

Functional Group Chemistry

3.8

Alkanes

3.9

Alcohols

3.10

Halogenoalkanes

4

Reactivity - What Drives Chemical Reaction?

5

Reactivity - How Much, How Fast & How Far?

6

Reactivity - The Mechanisms of Chemical Change

7

Measurement, Data Processing & Analysis

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