Difference Between Ionization and Dissociation

Main Difference – Ionization vs Dissociation

Ionization and dissociation are two related terms that express almost the same meaning but are used at different occasions. Ionization may refer to different types of separations. It can be ionization of atoms by removal of electrons or the formation of ions in a liquid solution. Dissociation, on the other hand, is the separation a substance into smaller constituents such as atoms, ions or radicals. The main difference between ionization and dissociation is that ionization always forms electrically charged particles whereas dissociation may or may not form electrically charged particles.

Key Areas Covered

1. What is Ionization
      – Definition, Explanation
2. What is Dissociation
     – Definition, Explanation, Dissociation Constant
3. What is the Difference Between Ionization and Dissociation
     – Comparison of Key Differences

Key Terms: Atom, Dissociation, Dissociation Constant, Electrons, Ionic Compound, Ionization, Ionization Energy, Ion Pairs, Radiation, Radical

Difference Between Ionization and Dissociation - Comparison Summary

What is Ionization

Ionization is the process by which atoms or molecules get a positive or negative charge. This occurs due to either gaining or losing electrons from atoms or molecules, and the resulting ions can be either cations or anions. Loss of electrons from a neutral atom or molecule forms a cation and the gain of electrons from a neutral atom gives it a negative charge, forming an anion.

The ionization of atoms occurs due to the removal of electrons from the atom. When an electron is removed from a neutral, gaseous atom by addition of energy, it forms a monovalent cation. The amount of energy required for this is known as first ionization energy of that atom.

Difference Between Ionization and Dissociation

Figure 1: Ionization Energies of Some Elements

Ionization that takes place in a liquid solution is the formation of ions in the solution. For example, when HCl molecules are dissolved in water, hydronium ions (H3O+) are formed. Here, HCl reacts with water molecules and forms positively charged hydronium ions and negatively charged chloride (Cl) ions.

Ionization may occur by collisions. This occurs mainly in gases when an electric current is passed through the gas. If the electrons in the current have the sufficient amount of energy required to remove electrons from gas molecules, they will force out electrons from gas molecules, producing ion pairs that consist of the individual positive ion and the negative electron. Here, negative ions may be formed as well because some electrons tend to attach to gas molecules rather than pulling electrons out.

Ionization occurs when radiation energy or sufficiently energetic charged particles are passed through solids, liquids or gases; for example, alpha particles, beta particles, and gamma radiation can ionize substances.

What is Dissociation

In chemistry, dissociation is the breakdown of a substance into smaller particles such as atoms, ions or molecules. These smaller particles are usually capable of recombining together at given conditions. Dissociation may occur forming atoms, ions or radicals.

The major causes for dissociation are the addition of solvent and the addition of energy in the form of heat. When an ionic compound is dissolved in water, it is dissociated into its ionic constituents. When NaCl is dissolved in water, the resulting solution contains Na+ cations and Cl anions.

Main Difference - Ionization vs Dissociation

Figure 2: Acetylsalicylic Acid Dissociation

Dissociation Constant

Dissociation constant is the ratio between the concentrations of products and the reactant concentration after dissociation. This has a constant value if the temperature is constant. Let us consider an example, water.

H2O       ↔      H+    +   OH

The dissociation constant of water is then,

Kw    =    [H+][ OH] / [H2O]

Difference Between Ionization and Dissociation

Definition

Ionization: Ionization is the process by which atoms or molecules get a positive or negative charge.

Dissociation: Dissociation is the breakdown of a substance into smaller particles such as atoms, ions or molecules.

Concept

Ionization: Ionization is the formation of ions.

Dissociation: Dissociation is the formation of small constituents from larger compounds.

Theory

Ionization: Ionization occurs when an atom or a molecule gains or loses an electron (or few electrons).

Dissociation: Dissociation occurs with the addition of solvent and the addition of energy in the form of heat.

End Product

Ionization: Ionization always forms ions in the end.

Dissociation: Dissociation forms atoms, ions or molecules that are smaller than the starting material.

Conclusion

Ionization and dissociation basically express the same theory: separation of constituents. The main difference between ionization and dissociation is that ionization always forms electrically charged particles whereas dissociation may or may not form electrically charged particles.

Reference:

1. “Ionization.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 17 Oct. 2016, Available here.
2. “Dissociation.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 7 Dec. 2011, Available here.
3. “Dissociation constant.” Wikipedia, Wikimedia Foundation, 22 Jan. 2018, Available here.

Image Courtesy:

1. “Ionization energy of alkali metals and alkaline earth metals” By DePiep – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Acetylsalicylic acid dissociation” By Fvasconcellos 19:57, 7 September 2007 (UTC) – Own work, after Image:Asa acid dissociation 342.jpg by Bfesser (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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