The distinction between atomic number and the mass number is the atomic number is the number of protons in nucleus of an atom. The distinction between mass number and atomic mass is the atomic mass defined is AMU (atomic mass units). Mass number is the total number of protons and neutrons in a nucleus.
Work Step by Step
Atomic number is generally shown above the element symbol in the periodic table. Atomic mass is shown below the element symbol in the periodic table. AMU is defined as 1/12 the mass of carbon-12. In other terms it is usually the same as the amount of protons and neutrons added together for a said element. Mass number is not shown in the periodic table but it is calculated by adding the number of neutrons and protons. (take the atomic mass and subtract the atomic number from it obtain the number of neutrons).