The Valley or Band of Stability represents the area where stable, non-radioactive isotopes exist based on their ratio of neutrons to protons.
Valley of Stability
Whenever the difference between neutrons to protons within a nucleus is significant enough an isotope is radioactive.
Concept #1: The central idea of nuclear chemistry is that unstable nuclei will give off radiation.
Neutrons act like the glue that keeps the nucleus together. The more neutrons present then the greater the attractive strong force, while the more protons then the greater the repulsive Coulombic force.
Concept #2: Non-radioactive isotopes with the optimum number of neutrons to protons will lie within the Valley of Stability, while radioactive isotopes will lie outside of it.
Example #1: Determine if the following nuclide will undergo alpha decay, beta decay or positron emission.
Hydrogen-3
Example #2: Determine if the following nuclides will undergo alpha decay, beta decay or positron emission.
Radon-222
Example #3: Determine if the following nuclides will undergo alpha decay, beta decay or positron emission.
Magnesium-50