Atoms of the same element having same atomic number but having different atomic masses are called isotopes.
According to Dalton’s atomic theory, all the atoms of an element are alike in all the properties including their masses. Later on, it was discovered that atoms of the same element may be different from each other. These are called isotopes.
Discoverer:
The phenomenon of isotopy was discovered by Soddy.
Properties and position in periodic table:
Since the electronic configuration of isotopes of an element is the same, therefore they possess the same chemical properties and occupy the same position in the periodic table.
Composition:
Isotopes of an element have the same number of protons and electrons but have different number of neutrons in their nuclei.
Example — Isotopes of Hydrogen
For example, each of the three isotopes of hydrogen i.e., protium (H), deuterium (H) and tritium
Protium H
At. No. = 1
No. of electrons = 1
No. of protons = 1
No. of neutrons = 0
At. Mass = 1
Deuterium H
At. No. = 1
No. of electrons = 1
No. of protons = 1
No. of neutrons = 1
At. Mass = 2
Tritium H
At. No. = 1
No. of electrons = 1
No. of protons = 1
No. of neutrons = 2
At. Mass = 3
Carbon, Nickel, calcium, palladium, cadmium and tin have 3,5,6,6, 9 and 11 isotopes, respectively.
