What is Ionization?
Ionization (or ionisation) is defined as the process by which an atom or molecule acquires a positive or negative charge by gaining or losing electrons, often in conjunction with other chemical changes. After ionization, the resulting electrically charged atom or molecule is known as an ion.
When particular chemical substances are added to water – for example, sodium chloride (NaCl) – they get dissolved and their molecules get split into negative and positive ions.
This process of splitting up molecules into positive and negative ions in solution is known as the ionization process.
The process of ionization is broken down step-by-step below.
What is the Ionization Process?
To understand the Ionization process, we will consider the structure of sodium chloride (NaCl). Sodium chloride is the common salt, we use in our day to day life.
The atomic number of Na and Cl are 11 and 17 respectively.
That means the sodium atom has 11 electrons and the chlorine atom has 17 electrons orbiting them.
The atomic structure or arrangement of these electrons is shown in the figure below.
As you can see above, the Na atom (left side of the figure) has only one single electron in its outermost orbit.
Whereas the chlorine (right side of the figure) contains seven electrons in its outermost orbit.
To remain stable, atoms generally require eight electrons in their outermost orbit.
So, both of the shown atoms are “unstable” (also known as “chemically active”).
When these two atoms are brought together, the Na atom loses its outermost electrons and becomes positively charged (because now it has more protons than electrons).
Conversely, the Cl atom gains one electron and becomes negatively charged (because now it has more electrons than protons).
So both atoms obtain eight electrons in their outermost orbit by exchanging these electrons.
As the Na atom is positively charged and the Cl atom is negatively charged, an electrostatic force acts between them, due to which they will together and make one NaCl molecule.
According to Coulomb’s law, the electrostatic force acting between two opposite charges is expressed as:
Where εr is the relative permittivity of the medium.
Hence the electrostatic force between the two charges is inversely proportional to the relative permittivity of the medium in which the charges are placed.
The ionization process can easily be explained by the relative permittivity of the medium. The relative permittivity of air is 1.00058986 ± 0.00000050 or 1 and the relative permittivity of water at 20oC is 80.
So, in water, the electrostatic force acting between Na and Cl is 80 times smaller than that in the air.
The electrostatic force between Na and Cl becomes so small, that it becomes difficult to hold the Na and Cl together in the water.
That is why whenever NaCl (sodium chloride) is dissolved in water, its molecules split into the positive Na ion and negative Cl ion — even at or below room temperature.
This is the ionization process of NaCl.
Ionization Process – Explained on Video
For those who prefer a video explanation, the video below explains what ionization is, and the ionization process of sodium chloride.