Key Concepts: Electrons, Protons & Neutrons

Core Definitions

• Proton: A positively charged subatomic particle found in the nucleus; defines the element (atomic number).
• Neutron: A neutral subatomic particle found in the nucleus; contributes to atomic mass.
• Electron: A negatively charged particle orbiting the nucleus in energy levels; very small mass.
• Atomic Number: The number of protons in an atom; identifies the element.
• Mass Number: The total number of protons + neutrons in the nucleus.
• Charge Balance: In a neutral atom, the number of protons equals the number of electrons.