Physics: Nuclear Physics - Atomic Nuclei, Isotopes, and Nuclear Stability

The nucleus is the small, dense, positively charged center of an atom, containing protons ($p^{+}$) and neutrons ($n^{0}$), which are collectively known as nucleons.

The Atomic Number ($Z$) represents the number of protons in the nucleus and defines the identity of the chemical element.

The Mass Number ($A$) is the total number of protons and neutrons in the nucleus. The relationship is given by $A = Z + N$, where $N$ is the number of neutrons.

Isotopes are atoms of the same element that have the same number of protons ($Z$) but a different number of neutrons ($N$), resulting in different mass numbers ($A$).

Chemical properties of isotopes remain identical because they have the same electron configuration, but their physical properties (like density or boiling point) may differ due to mass differences.

Nuclear Stability is maintained by the Strong Nuclear Force, which acts over very short distances to overcome the electrostatic repulsion between positively charged protons.

For light nuclei (up to $Z \approx 20$), the ratio of neutrons to protons ($N:Z$) is typically $1:1$ for stability. As the atomic number increases, more neutrons are needed to provide enough strong force to keep the nucleus stable.