* Protons: These particles have a positive charge and are found in the nucleus of an atom. They have mass and are included in the calculation of atomic number.
* Neutrons: These particles have no charge (they are neutral) and are also found in the nucleus. They have mass and are not included in the calculation of atomic number.
* Electrons: These particles have a negative charge and orbit the nucleus. They have very little mass (almost negligible compared to protons and neutrons) and are not included in the calculation of atomic number.
Key Takeaway: The atomic number of an element is defined solely by the number of protons it has. This number determines the element's identity.
