Question 2: Why do heavier elements require more neutrons in order to maintain stability?

ANSWER

Nucleons (protons and neutrons) are subjected to two forces in the nucleus.

• Coulomb’s force of repulsion among the protons.
• Strong force of attraction among all the nucleons; proton and proton, proton and neutron and neutron and neutron.

The strong force is a short range force. It acts in a small range and beyond that range its effect is negligible or non-existent. On the other hand, Coulomb force is effective to a comparatively longer distance.

In the small range (very short distance) the attractive strong force is dominant over the Coulomb force of repulsion. However, in the long range, the Coulomb force becomes stronger.

Heavier nuclei have larger number of nucleons. The separation among the particles also increases with the increase in the volume. Consequently, the Coulomb force of repulsion is likely to override the attractive strong force. Therefore, the nucleus becomes unstable.

When the number of neutron increases, it adds to the stability of the nucleus. Because in this way the strong force increases which combines the nucleons in the nucleus. Because with the increase of neutrons, the attractive force among all particles increases.

Therefore, for the stability of a nucleus, we need greater number of neutrons.