Question

Why is binding energy for heavy nuclei low?

Answer 1

Hint :We know that the binding energy per nucleon is a measure of stability of an atom. More the Binding energy per nucleon in nuclei more will be its stability. It is natural for an element to attain stability and reach a higher Binding energy per nucleon.

Complete Step By Step Answer:
Nucleons of a nucleus are nothing but the collection of neutrons and protons in a nucleus. To hold these neutrons and protons in a nucleus together, a certain amount of energy is required. This energy also determines the stability of a nucleus. We can say that this energy is the binding energy of the electron to the nucleus (though we strictly use the term ionization energy). In the case of a nucleus, binding energy is the amount of energy required to separate all the protons and neutrons constituting that nucleus. It can be also said that binding energy is the amount of energy given to bring all those protons and neutrons to make that nucleus. If we simply divide this binding energy by the amount of nucleons (protons with neutrons) we get binding energy per nucleon.
The collections of subatomic particles or component parts which constitute a nucleus in an atom are called nucleons. These component parts of a nucleus are nothing but neutrons and protons. Nucleons of a nucleus are held together by strong attractive forces among themselves. These strong attractive forces bind the nucleons together to make the nucleus stable. When a heavy nucleus breaks down to its constituent nucleons, it is seen that the binding energy per nucleon is higher than the binding energy of the nucleus itself.
This suggests that nucleons are tightly bound after the breakdown. Similarly, when two light nuclei fuse to form a heavy nucleus, it is seen that the binding energy per nucleon of the heavy nucleus is higher than the binding energy per nucleon of lighter nuclei. This suggests that nucleons are tightly bound, after the fusion between two light nuclei to form a heavy nucleus. For heavy nuclei, the protons on either side of the nucleus repel each other due to electrostatic repulsion. Hence the nuclear force becomes weak at this distance. Therefore, the average binding energy is very less.

Note :
Remember that the nuclear forces are short-range forces. The force exerted by a nucleon inside a nucleus is short-ranged. This suggests that binding energy caused by a nucleon will have an effect only on that particular nucleon’s immediate neighbors.