What is the unit mass of an atom on the periodic table?
The unit mass for an atom (element) on the periodic table is not a whole number. It is a decimal number due to the fact that there are different isotopes for each element, and the atomic weight is a weighted average of all the isotopes for that element and their relative abundance.
The atomic weight or relative atomic mass does not really have units, but scientists have given them units, such as the atomic mass unit, amu; unified atomic mass unit, u; or the Dalton, Da, as an alternative symbol for the unified atomic mass unit. One u is