You've raised an interesting point, but in reality, heavy atoms tend to have more neutrons than light atoms, rather than fewer. Let's delve into the reasons behind this:
Stability and Nuclear Forces: The stability of an atomic nucleus is influenced by the balance between the nuclear forces that hold it together and the electrostatic repulsion between protons. Protons, being positively charged, experience electrostatic repulsion, which can potentially destabilize the nucleus. Neutrons, on the other hand, do not experience this repulsion. By increasing the number of neutrons relative to protons, the nuclear forces can better counteract the electrostatic repulsion, enhancing the overall stability of the nucleus.
Binding Energy: The total binding energy of a nucleus plays a significant role in its stability. The binding energy is the energy required to break apart the nucleus into its constituent protons and neutrons. It is found that for most stable nuclei, the binding energy per nucleon (proton or neutron) is maximized around a certain range of mass numbers. As the mass number increases, adding more neutrons to the nucleus can contribute to an increase in the total binding energy and, hence, enhance stability.
Strong Nuclear Force: The strong nuclear force, which is responsible for holding protons and neutrons together, acts on both protons and neutrons. However, since neutrons have no electric charge, they are not subject to the repulsive forces experienced by protons. This allows neutrons to contribute to the overall nuclear stability without adding to the electrostatic repulsion.
Beta Decay: In heavier elements, some of the neutrons can undergo beta decay, transforming into protons while emitting an electron and an antineutrino. This process converts neutrons into protons, leading to an increase in the proton count and a decrease in the neutron count.
It is worth noting that the precise balance of protons and neutrons in an atomic nucleus depends on the specific element and is determined by various factors, including the interplay of nuclear forces, binding energy considerations, and the process of beta decay.