The ratio of the average mass per atom of an element to 1/12 of the mass of nuclide 12C. An atomic weight can be defined for a sample of any given isotopic composition. The standard atomic weight refers to a sample of normal terrestrial isotopic composition. The term relative atomic mass is synonymous with atomic weight.
The relative atomic mass is the number of times heavier an atom is compared to one twelth of a carbon-12 atom. The periodic table
average mass of the atoms of the isotopes of a given element as they occur naturally. The isotopes of a given element have atoms with the same number of protons but different numbers of neutrons