Find protons, neutrons, and electrons from atomic and mass numbers.
An atom consists of a nucleus (protons + neutrons) surrounded by electrons. The atomic number (Z) = number of protons = number of electrons in a neutral atom. The mass number (A) = protons + neutrons. Neutrons = A - Z. For ions, electrons = Z - charge (cations lose electrons, anions gain them). Isotopes of the same element have the same Z but different A (different neutron counts). For example, Carbon-12 (6p, 6n) and Carbon-14 (6p, 8n) are both carbon (Z=6) but different isotopes. The nucleus contains >99.95% of an atom's mass. If an atom were a football stadium, the nucleus would be a marble at the center — the rest is empty space filled with electron probability clouds.