The A is the atomic mass and the Z is the atomic number of our element. Now the atomic mass is the mass of that element. It's the number of protons and the number of neutrons. Now note that electrons are not counted Naratomic mass because their mass is much smaller than that the proton or the neutron. Now the atomic number is the number of protons of our element. Now that number, the atomic number is the identity number of that element.