Like many things in chemistry there are observed patterns of stability.

In general:

  • Too many or two few neutrons result in an unstable nucleus.
  • Unstable isotopes undergo nuclear decay. The rate of decay is expressed by the isotope's half-life.
  • Elements with an atomic number greater than 83 are not stable and are considered radioactive.
  • Increasing temperature or pressure does not increase the rate of nuclear decay for radioactive isotopes.