3.48 What is the molecular formula of each of the following compounds?
(a) empirical formula HCO2, molar mass = 90.0 g/mol
(b) empirical formula C2H4O, molar mass = 88 g/mol

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.