The structure of an atom and its nucleus is a fundamental concept in physics. Atoms are composed of a central nucleus containing protons and neutrons, surrounded by orbiting electrons. The nucleus determines the atom's identity (atomic number) and most of its mass, while the electrons are responsible for chemical behavior. Nuclei themselves can undergo various transformations, including radioactive decay
Nucleus: The dense, positively charged center of the atom, containing protons (positively charged) and neutrons (neutral)