Question

State the general rules for predicting nuclear stability.

Short answer

The general rules to predict nuclear stability involve recognizing 'magic numbers' of protons or neutrons, maintaining a proper neutron to proton ratio, having an even number of protons and neutrons, staying within the band of stability, and considering the concept of 'Islands of Stability' for superheavy elements.

Step-by-step solution

Rule 1: Magic Numbers

The nuclei are observed to be most stable when the number of protons or neutrons it has is equal to any of the 'magic numbers': 2, 8, 20, 28, 50, 82, or 126. These specific numbers of protons or neutrons have higher binding energies which contribute to a nucleus's stability.

Rule 2: Neutron to Proton Ratio

For lighter elements (atomic number less than or equal to 20), stable nuclei have a neutron to proton ratio close to 1:1. But for heavier elements (atomic number greater than 20), the neutron to proton ratio increases as atomic number increases. This is because neutrons help to cushion the repulsive forces between protons in the nucleus, which are greater for elements with larger atomic numbers.

Rule 3: Even-Even Nuclei

Nuclei with an even number of both protons and neutrons are observed to be more stable. This can be explained by the pairing effect, which states that particles (like protons and neutrons) tend to pair up, resulting in increased stability.

Rule 4: Band of Stability

The band of stability is a region on a graph of Neutrons (N) versus Protons (Z) where stable nuclei are found. Nuclei outside of the band are unstable and undergo radioactive decay until they reenter the band.

Rule 5: Islands of Stability

There is a theoretical concept known as the 'Island of Stability' which pertains to superheavy elements. It suggests that certain superheavy nuclei with specific 'magic numbers' of protons and neutrons may have longer half-lives as a result of increased nuclear stability.