Question

Distinguish between isotopes and isobars, giving one example for each.

Hint:

Memory key:
Isopopes $\rightarrow$ Same proton number $Z$.
Isobars $\rightarrow$ Same atomic mass number $A$.
Isotones $\rightarrow$ Same neutron number $N$.

Answer 1

Concept:
• Nuclides are classified based on atomic number $Z$ (proton count), neutron number $N$, and mass number $A = Z + N$.

Step 1: Define Isotopes
Isotopes are nuclides belonging to the same chemical element that have the same atomic number ($Z$) but different mass numbers ($A$).
- They contain identical numbers of protons but different numbers of neutrons ($N = A - Z$).
- They possess identical chemical properties because chemical behavior is dictated by atomic number $Z$.
- Example: Isotopes of Hydrogen: Protium ($\text{}^{1}_{1}\text{H}$), Deuterium ($\text{}^{2}_{1}\text{H}$), and Tritium ($\text{}^{3}_{1}\text{H}$). Alternatively, Carbon isotopes: $\text{}^{12}_{6}\text{C}$ and $\text{}^{14}_{6}\text{C}$.

Step 2: Define Isobars
Isobars are nuclides belonging to different chemical elements that have the same mass number ($A$) but different atomic numbers ($Z$).
- They contain different numbers of protons and neutrons, but their total nucleon sum ($Z + N$) is equal.
- They possess distinct chemical properties because their atomic numbers $Z$ are different.
- Example: Argon ($\text{}^{40}_{18}\text{Ar}$) and Calcium ($\text{}^{40}_{20}\text{Ca}$). Alternatively, Carbon ($\text{}^{14}_{6}\text{C}$) and Nitrogen ($\text{}^{14}_{7}\text{N}$).

Step 3: Conclusion
Isotopes share the same $Z$ but different $A$ (same element), whereas Isobars share the same $A$ but different $Z$ (different elements).