• Focuses on changes within atomic nuclei.
• An atom is the smallest unit of an element, made up of protons, neutrons, and electrons.

Atomic Structure:

• Protons: Positively charged particles located in the nucleus.
• Electrons: Negatively charged particles orbiting the nucleus at high speed with negligible mass.
• Neutrons: Neutral particles with no overall charge, located in the nucleus.

Nuclear Notations:

• Atomic number (Z): Represents the number of protons in the nucleus and equals the number of electrons in a neutral atom. It identifies the element.
• Atomic mass (A): The total number of protons and neutrons (nucleons), calculated as A = Z + N, where N is the number of neutrons.

Representation:

• An atom is denoted as , where:
  • X = element symbol,
  • A = atomic mass,
  • Z = atomic number.