No, the stability or instability of a nucleus does not solely depend on whether the atomic number (Z) is even or odd. While it is true that many elements with even atomic numbers have stable nuclei, and some elements with odd atomic numbers have unstable nuclei, there are exceptions and other factors that influence nuclear stability.
Nuclear stability primarily depends on the balance between the strong nuclear force and the electromagnetic force within the nucleus. The strong nuclear force holds the protons and neutrons together, while the electromagnetic force, specifically the repulsion between positively charged protons, tries to push the nucleus apart.
There are a few factors to consider when assessing nuclear stability:
Magic Numbers: Certain numbers of protons or neutrons, known as magic numbers (2, 8, 20, 28, 50, 82, 126), tend to result in more stable nuclei. These numbers correspond to the filling of specific energy levels within the nucleus. Elements with an even number of both protons and neutrons, such as helium-4 (2 protons and 2 neutrons) and oxygen-16 (8 protons and 8 neutrons), often exhibit greater stability due to these magic numbers.
Nuclear Shell Model: The nuclear shell model describes the behavior of nucleons (protons and neutrons) in energy levels or shells within the nucleus, similar to the electron shells in an atom. Just like the electron configuration affects the stability of atoms, the arrangement of nucleons in specific shells impacts nuclear stability. When the shells are filled or half-filled, the nucleus tends to be more stable.
Nuclear Forces: The strength and interplay of the strong nuclear force and the electromagnetic force influence nuclear stability. If the repulsive electromagnetic force between protons becomes dominant due to a high proton-to-neutron ratio or excessive total nuclear charge, the nucleus can become less stable. However, the presence of additional neutrons can counteract this instability, as neutrons do not contribute to electromagnetic repulsion.
In summary, while there is a general trend of greater nuclear stability for elements with even atomic numbers and specific proton-neutron ratios, other factors such as magic numbers, the nuclear shell model, and the balance of nuclear forces play significant roles in determining the stability or instability of a nucleus.