What are Isobars?

By BYJU'S Exam Prep

Updated on: September 25th, 2023

The atoms of various elements with various atomic numbers having the same mass number are called as isobars. They have different electronic configuration.


  • Atoms of various elements with various atomic numbers but the same mass number are called isobars.
  • Isobars have different electronic configuration.

Examples of Isobars

  • Argon Ar 1840, potassium K 1940, and calcium Ca 2040 are examples of isobars.
  • Here, the atomic numbers of argon, potassium, and calcium are 18, 19, and 20, respectively.
  • The mass number of all the atoms described above is 40. Their atomic numbers, however, differ.
  • They are categorised as isobars as a result.
  • The atomic numbers of carbon and nitrogen are 6 and 7, respectively.
  • Since nitrogen and carbon-14, an isotope of carbon, share the same mass number (14), they are isobars.

Table of content


Electronic Configuration for Isobars:

  • Take an example of a pair of isobar i.e.,4020Ca and 4018Ar
  • The electronic configuration of isobar 4020Ca is 2,8,8,2
  • The electronic configuration of isobar 4018Ar is 2,8,8.
  • Both isobars’ electronic configurations are different.
  • because the two isobars’ electron densities differ.


What are Isobars?

Isobars are atoms of different elements with different atomic numbers and the same mass number. Their electronic setups are different.

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