1.1.6—Determine the numbers of protons, neutrons

Read isotope notation ^A_ZX by taking A as the mass (nucleon) number and Z as the atomic (proton) number. X identifies the element symbol; the two numbers give the nuclear particle counts.

Proton number = Z. Neutron number = A − Z. The mass number counts only protons and neutrons, so it is the total number of nucleons in the nucleus.

For a neutral atom, electron number = Z. For an ion, adjust the electron count for the stated charge: a positive charge means electrons have been lost, while a negative charge means electrons have been gained.

Use a fixed sequence: read A and Z, calculate A − Z for neutrons, then use the charge only to adjust electrons. Keep the element identity tied to Z; changing electron number changes charge, not the element.