Which element on the periodic table has the greatest atomic mass?

Why isnt relative atomic mass of an element used to characterise it in the periodic table?

• this is a question i am really confused about. The answer is something to do with the isotopes of each element but i dont know how to put it in words Thanks for ur help much appreciated :-)

• Answer:

  The first periodic tables listed the elements in order of increasing atomic weight. After Moseley discovered that atomic number gave a better match to the x-ray data, the periodic table made more sense when it was arranged by atomic number. The atomic weights printed on the periodic table are, for the most part, not the actual weights of any atom, but instead, are the weighted averages of the different weights of the isotopes of that element. About 20+ elements have only one naturally occurring isotope, and so for those elements the atomic weight really is the weight of an atom of that element.