Question

Why are all elements above $82$ are unstable?

Answer 1

Binding energy:

1. The total number of protons and neutrons in an atomic nucleus is known as an atom's mass number or its nucleon number.
2. Atoms are not stable when their mass number is higher than $82$ due to the amount of binding energy present.
3. Binding energy is the force keeping a nucleus together.
4. When protons are added with an increase in mass number they are close to one another due to which protons exhibit strong electrostatic (like-kind repel) forces that's why the nucleus cannot hold together.
5. The force of repulsion between the particles causes the atom to split, and the new elements are created as they reach a new, stable configuration.

Therefore, all elements above $82$ are unstable because of repulsion forces between protons.