Remember that the atomic number is the same as the number of protons which you have already identified. It is represented by A and is also known as the nucleon number. Pin En Useful Things Number of protons present in an atom. . The period number on the Periodic table tells you the total number of orbits that the atom will have. A pure substance that cannot be broken down into a simpler substance by chemical means. Thus the atomic number of Na atom number of electrons number of protons 11. There are 275 isotopes of the 81 stable elements in addition to over 800 radioactive isotopes and every element has known isotopic forms. A n Z. How to find the Atomic Mass. Force definition physical power or strength possessed by a living being. For example hydrogen-3 atomic number 1 mass number 3 decays to helium-3 atomic number 2 mass number 3. Thus negative beta decay results in a daughter nucleus the proton number a...