Nuclear Physics - The nuclear model of the atom

The Rutherford alpha-particle scattering experiment: Most $\alpha$-particles passed through gold foil undeflected, showing the atom is mostly empty space. A small number were deflected at large angles, proving the existence of a tiny, dense, positively charged nucleus.

Atomic structure: The atom consists of a central nucleus containing protons and neutrons, surrounded by electrons orbiting in shells.

Protons: Relative mass of $1$, relative charge of $+1$. The number of protons is the atomic (proton) number $Z$.

Neutrons: Relative mass of $1$, relative charge of $0$. These are found in the nucleus and provide stability.

Electrons: Relative mass of $\frac{1}{1836}$ (negligible), relative charge of $-1$. In a neutral atom, the number of electrons equals the number of protons.

Nuclide notation: Represented as $^{A}_{Z}X$, where $A$ is the nucleon (mass) number and $Z$ is the proton (atomic) number.

Isotopes: Atoms of the same element with the same number of protons ($Z$) but different numbers of neutrons (different $A$). They share identical chemical properties due to having the same electron configuration.