Every atom seeks to be as stable as possible. In the case of radioactive decay, instability occurs when there is an imbalance in the number of protons and neutrons in the atomic nucleus. ... If the nucleus of an atom is unstable, eventually it will break apart to lose at least some of the particles that make it unstable.

Why do isotopes decay?

Certain naturally occurring radioactive isotopes are unstable: Their nucleus breaks apart, undergoing nuclear decay. ... All elements with 84 or more protons are unstable; they eventually undergo decay. Other isotopes with fewer protons in their nucleus are also radioactive.

Can unstable isotopes decay?

Sometimes isotopes decay from one unstable isotope into another unstable isotope. This can happen continuously in a long radioactive chain. An example of a radioactive chain is uranium-238. As it decays, it transforms through a number of elements including thorium, radium, francium, radon, polonium, and bismuth.