The ionization energy of an elements in the minimum energy required to remove an electron from its gaseous atom to form an ion. This process is called ionization energy
In the gaseous phase, the atom and ions are isolated and are free from all external influences. Thus, the ionization energy is the qualitative measure of the stability of an isolated atom.
The ionization energy of some elements are given below.
Factor Influences the Ionization Energies
It is observed that the ionization energies of atom depend upon the following factors.
Variation of Ionization Energy in the Periodic Table
In the periodic table, the ionization energies changes in the periods and in the group differently.
In the periodic table, the ionization energies increase from left to right in a period with increase in the proton number, until the maximum value is reached at the end of the periods.
This can be explained in term of periodicity of the electronic configuration of the elements. Each period is begins with an element which has one electron in its valence shell and ends with the completion of an electronic shell.
The increase in the atomic number is associated with the increase in nuclear charge which leads to a stronger force of attraction between nucleus and the increasing number of electron. The stronger force of attraction, ultimately result in difficult removal of electron.
In groups of the periodic table, the ionization energies decreases in spite of the increase in proton number or nuclear charge. This is due to successive addition of electronic shell as a result of which the valence electrons are placed at a larger distance from the nucleus.
As the force of attraction between the nucleus and the outer electron decreases with the increase in distance, the electron can be removed more easily or with less energy. Moreover, the force of attraction also decrease due to increasing shielding effect of the intervening electrons.
The ionization energies of the group 3-A and 4-A show abnormal trend. This can be understood from the distribution of electrons.
Higher Ionization Energies
So far, we have explained the first ionization energy.The energy required to remove an electron after the removal of first electron is called Second ionization energy.
The second ionization energy of Mg is 1450 kJ/mole
Similarly, the energy required to remove third electron after the removal of second one is called Third ionization energy.
The third ionization energy of Mg is 7730 kJ/mole.
It means that the ionization energy value undergo an increase with increase in the number of electrons to be removed. This is due to the reason that second electron is removed from the positively charged ion rather than a neutral atom. The dominant positively charged holds the electron more tightly and thus further removal of electron become more difficult.
Ionization energy is an index to the metallic character. The elements having low ionization energies are metals and those having high ionization energies are non-metals. Those with the intermediate values are mostly metalloids.
The gaps in the first, second, third and higher ionization energies help us to guess the valency of an element. If there is sufficiently gap between first ionization and second ionization, then the element show valency of one.
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