# Why is it that only isotopes tend to be radioactive?

Jul 21, 2014

Every natural element consists of isotopes.

Even hydrogen, the smallest atom, has three isotopes: $\text{_1^1"H}$, $\text{_1^2"H}$, and $\text{_1^3"H}$.

Of these, the first two are stable. The third, tritium, is radioactive.

Thus there are two kinds of isotopes — stable isotopes and radioactive isotopes.

To be stable, a nucleus should contain about the same number of neutrons as protons.

The chart above shows that there are many more radioactive isotopes than stable isotopes.