Aug 6, 2017

Isotopes have same atomic numbers but different mass numbers or we can say same number of protons but different no of neutrons, on the other hand isobars have different number of protons but same number of nucleons (protons and neutrons combined) or we can say different atomic numbers but same mass numbers.

Aug 6, 2017

An isotope is an atom of an element with a differing number of neutrons. That is to say, elements typically have multiple isotopes, each with a different number of neutrons, but they all have the same number of protons if the element is the same.

For example, hydrogen has $3$ naturally-occurring isotopes, $\text{^1"H}$ (called protium), $\text{^2"H}$ (called deuterium), and $\text{^3"H}$ (called tritium). These three nuclides have the same number of protons (same element), but have different number of neutrons ($0$, $1$, and $2$ respectively).

An isobar is where different elements have the same number of nucleons (protons and neutrons collectively).

For example, $\text{^40"Ca}$ and $\text{^40"K}$ are isobars, because their mass number (number of nucleons) is the same, but they differ in the number of protons (and neutrons).