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Isotopes, Isobars and Isotones


  • These are elements which have the same atomic number but different atomic mass.
  • They have the same atomic number because the number of protons that are inside their nuclei remains the same.
  • But, they have different atomic mass because the number of neutrons that are also inside their nuclei is different.
  • As the number of protons inside nuclei remains same, therefore the overall charge of the elements also remains same as in isotopes: no of protons = no of electrons.
  • Hence, as isotopes overall charge remains neutral, therefore their chemical properties will also remain identical. 
Therefore, Isotopes are chemically same but physically different.

Examples of isotopes are:
1) Isotopes of hydrogen  
2) Isotopes of carbon 


  • These are elements which have same atomic mass but a different atomic number.
  • Hence, as isobars have different atomic number, therefore, they have a different number of electrons, and their chemical properties are different.
  • The light nuclei have unstable isobars.
  • Heavy nuclei have stable isobars and these occur in pairs.
  • If the number of protons of one isobar matches with that of another, then they are called as mirror-nuclides of each other

Therefore,  Isobars are chemically different but physically same.



These are elements having the same number of neutrons.

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