Isobar

Last revised by Dr Jeremy Jones on 29 Sep 2021

Isobars are atomic species that have the same mass number (A), but a different atomic number (Z).

Isobars should not be confused with isotopes, which share the same atomic number, and therefore belong to the same chemical element, but have varying mass numbers.

Examples of isobars include 14,6C; 14,7N; 14,8O. These atoms all have the same number of nucleons (14).

In nuclear physics, isobars tend to undergo beta decay.

A mnemonic that can be used to differentiate isotones from isotopes and isobars is as follows:

  • same Z (number of protons) = isotopes
  • same A (number of nucleons) = isobars
  • same N (number of neutrons) = isotones

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