Isobars are atoms of different elements that have the same mass number (A) but different atomic numbers (Z). Although they are completely different elements, they have the same total number of protons + neutrons.
Definition: Same mass number, different atomic number.
Famous Example: Ca-40 and Ar-40.
Difference from Isotope: Isotopes = same element, same Z, different A.
Memory Trick: Iso-BAR = same B(A)R (mass numbeR).
Calcium (Ca) and Argon (Ar) are the most famous isobars:
Both have a mass number of 40, but they are completely different elements.
| Property | Isotopes | Isobars |
|---|---|---|
| Same Element? | Yes | No (different elements) |
| Same Atomic Number (Z)? | Yes | No |
| Same Mass Number (A)? | No | Yes |
| Example | C-12 and C-14 | Ca-40 and Ar-40 |
Isobars are atoms of different elements that have the same mass number but different atomic numbers.
Calcium-40 and Argon-40 are isobars — both have mass number 40, but Calcium has atomic number 20 and Argon has atomic number 18.
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