The number of protons, neutrons, and electrons in an atom can be determined from a set of simple rules.
The number of protons in the nucleus of the atom is equal to the atomic number (Z).The number of electrons in a neutral atom is equal to the number of protons.The mass number of the atom (M) is equal to the sum of the number of protons and neutrons in the nucleus.The number of neutrons is equal to the difference between the mass number of the atom (M) and the atomic number (Z).Examples: Let's determine the number of protons, neutrons, and electrons in the following isotopes.12C 13C 14C 14N