Those atoms of the same element with different mass numbers are called Isotopes of that element.
In other words, atoms whose atomic numbers are the same but different mass numbers are called isotopes of each other.
Since the mass of an atom and its atomic weight are approximately equal. Therefore, the above definition of isotopes can also be written as this — atoms whose atomic numbers are the same but different atomic mass are called isotopes of each other.
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Examples of isotopes:
Three isotopes of the hydrogen element are known. Their atomic number is 1 and their mass numbers are 1, 2 and 3 respectively. These isotopes are called hydrogen-1 or protium, hydrogen-2 or deuterium and hydrogen-3 or tritium.
Their symbols are 1H1, 1H2, and 1H3 respectively. Each of them has 1 electron and 1 proton and the numbers of neutrons are 0, 1 and 2 respectively.
Features of isotopes:
The atomic numbers of isotopes are the same and the atomic mass are different.
In isotopes the numbers of electrons and protons are the same and the numbers of neutrons are different.
Since the atomic numbers of isotopes are similar, the chemical properties of isotopes are similar.
Example: Light hydrogen gets water when it is burnt in air. In the same way, when heavy hydrogen is burnt in air, heavy water is obtained.
Physical properties of isotopes vary (density, boiling point)
The number of neutrons in the nuclei of isotopes varies. Hence the nuclear structure of isotopes is different. The radioactive properties of isotopes may be different due to the differing nuclear structure.
Example: carbon-12 is not radioactive while carbon-14 exhibits radioactivity.
In Mendeleff’s original periodic table, elements were placed in increasing order of atomic weight. In 1913 Mozley proved that the basic characteristics of elements are not atomic weight but atomic number and the chemical properties of elements depend on their atomic number.
Therefore, in the modern periodic table, elements are placed in the increasing function of their atomic number, therefore all the isotopes of an element are kept in one place in the periodic table, and hence they are named isotopic.
There are two types of isotopes
1. Radioactive or permanent isotopes — The nuclei of these isotopes are permanent and do not disintegrate automatically. The three isotopes of carbon displayed in the table, carbon-12 and carbon-13 are not radioactive.
It is called radioactivity-less or permanent isotopic. Similarly, hydrogen-1 and hydrogen-2 are one of the three isotopes of hydrogen. Hydrogen is not radioactive.
2 Radioactive or temporal isotopes — The nuclei of these isotopes are temporary. For this reason, the nuclei of the isotopes themselves disintegrate.
As a result of dissolution, radioactive rays (α, β, and γ rays) and also types of nuclei or atoms are obtained. Only the isotopic 1H3 of hydrogen and isotopic 6C14 of the carbon shown in table represent radioactive.
Uses of isotopes
Isotopes are mainly used in the fields of scientific research, agriculture and medicine. The most prominent examples of the use of isotopes are those in which isotopes are used as investigative elements. The use of radioactive isotopes is prominent in these examples.