Atomic number - number of protons
Mass number = atomic number + number of neutrons
Relative isotopic mass - mass of isotope relative to 1/12th mass of an atom of C12
Relative atomic mass - weighted mean mass of an atom of an element relative to 1/12th mass of atom of C12
Weighted mean mass = relative isotopic mass x percentage abundance
for example, look at chlorine with atomic number 17, with relative atomic mass of 35.5. The periodic table uses relative atomic mass.
mass number is used with reference to a single atom/ion (to find the number of protons, neutrons, electrons using atomic number)