Chromium reacts with oxygen according to the equation: 4Cr + 3O2 à 2Cr2O3. Determine the moles of Cr that react with 21.53 moles of O2 .

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.