Magic numbers are an established number of nucleons (either neutrons or protons) that make a nucleus especially stable.
Whereas the Octet Rule relates stability to the number of valence electrons, the Magic Numbers relate the stability of the nucleus to the ratio of neutrons to protons.
Concept #1: Besides the ratio of neutrons to protons, the actual number of neutrons and protons will also affect the overall stability of the nucleus.
Concept #2: Just as elements with the ideal number of electrons depict unusually high stability so do elements with the ideal number of nucleons (# of protons and neutrons).
Example #1: Based on your knowledge of nuclide stability determine which of the following nuclides will be most stable.
a) Indium-115 b) Lanthanum-138 c) Calcium-40 d) Neodynium-144