Isotopes and Isobars

 

Isotopes and Isobars :-

Mass spectrometer is a device which is used for accurate measurement of atomic masses. From this device it was found that there exist some atoms of the same element, which exhibit the same chemical properties, but differ in mass. Such atomic species of the same element differing in mass are called isotopes.

Isotopes

Isotopes of an element are the atoms which have the same atomic number but different atomic masses.

Examples..

Isotopes of hydrogen, ₁H¹, ₁H², ₁H³

Isotopes of helium, ₂He³, ₂He⁴, ₂He⁶

Isotopes of carbon, ₆C¹⁰, ₆C¹¹, ₆C¹², ₆C¹³, ₆C¹⁴

Since isotopes of an element have the same atomic number, they contain same number of protons and same number of electrons but their atomic weights are different, so they contain different number of neutrons.

Practically every element consists of a mixture of several isotopes. The relative abundance of different isotopes differs from element to element.

The atomic weight of an element is the weighted average of the masses of all of its isotopes. For example Chlorine has two isotopes having masses 34.98 u and 36.98 u and their relative abundances in nature are 75.4% and 24.6% respectively.

∴ Average atomic weight of chlorine 

From here we can note that atomic weight may not be an integer but mass number A is always an integer because mass number represents the number of nucleons in the nucleus.

 

Isobars

Isobars are the atoms of different elements which have the same mass number but different atomic numbers.

They contain different number of protons, different number of electrons and different number of neutrons but the total number of nucleons in them is same.

Examples..

₁H³ and ₂He³

₁₁Na²² and ₁₀Ne²²

 

Isotones

The nuclides which contain the same number of neutrons(A-Z) are called isotones.

Examples..

₁H³ and ₂He⁴

₁₇Cl³⁷ and ₁₉K³⁹

 

 

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