[Chemistry Class Notes] Ionization Pdf for Exam

Ionization can be defined as when a neutral atom or molecule can be converted into electrically charged atoms by gaining or losing a free electron. Ionization happens during the process of a chemical reaction. To ionize an atom or a molecule, either loses or gains electrons―the electron which is either gained or lost forms an ion. 

The atom or molecule that gains an electron becomes negatively charged and is called the anion. On the other hand, the atom or molecule that loses a free electron becomes positively charged and is called the cation. In the process of ionization, energy is either released or gained.

Ionization Energy and Formation of Ions

In the process of ionization, when an atom gains an electron, it forms a negatively charged ion called an anion. In this process, there is a loss or release of energy. The energy so lost is called electron affinity. It is often observed that atoms with enormous electron affinity tend to gain electrons and form negatively charged ions. 

Similarly, to ionize, if an atom loses an electron, it forms a positively charged ion called a cation. In the process of electron loss,  a large amount of energy is absorbed. The energy so absorbed by the atom is called ionization energy. The ionization energy is the energy required to remove the electron from the orbit of the atom. It becomes easier to remove electrons from atoms with a minimal amount of ionization energy. 

In the periodic table, metals carry a small amount of ionization energy, and alkali metals have the lowest ionization energy. Hence, alkali metals are mostly found as positively charged ions in different chemical compounds. For example, we can find sodium cation, i.e. Na+ in sodium chloride (NaCl).

Electron Ionization

Electron Ionization, formerly known as Electron Impact Ionization, is an ionization technique in which energetic electrons are made to react with solids and gases to produce ions. It is also known as Electron Bombardment Ionization. The electron impact ionization was the first known technique of mass spectrometry. However, this method of ionization is still prevalent. 

The electron ionization technique is considered one of the most challenging techniques of ionization. The reason behind this is electron impact ionization uses highly energetic electrons to produce ions. The method is advantageous in the determination of the structure of unknown compounds. The technique also serves as a medium in detecting various other thermally stable and volatile compounds in solids, liquids and gases. 

Plasma Ionization

A plasma is simply an ionized gas. When a gas is put under high temperatures, the electrons are stripped away from the atoms of the gas, and thus it forms plasma. For ionization of plasma, high temperatures are required, and the gas is pumped with energy to allow the electron to move freely to form ions. The best example of plasma ionization can be the sun’s corona, where the Hydrogen gas reacts under high temperature to form a hydrogen ion and a free electron.

H  → H⁺ + e^– .

Ionization of Acids and Bases

Acids ionize in water. Strong acids can completely ionize in water, whereas weak acids can only ionize partially. The degree of ionization of acid can determine its strength. This method is also known as percent ionization. The method determines the extent to which an acid ionizes in water. If an acid ionizes completely, it is tagged as a strong acid, and if it ionizes partially, it can be termed as a weak acid.

In a similar way, bases ionize in an aqueous solution to produce hydroxide ions. The bases that dissociate entirely in solutions are called strong bases. On the other hand, the bases that don’t completely dissociate in an aqueous solution are called weak bases. Percent ionization is used to identify the strength of bases also.

Ionization of Water 

The ionization of water or self-ionization of water is an ionization process in which a water molecule, either in pure water or aqueous solution, ionizes itself to produce ions. The following equation can explain the self-ionization of water:

H₂O  ⇄  H₃O⁺  +  OH^–.

In the above reaction, the water molecule dissociates to form a hydronium ion and a hydroxide ion.