Part 1: Does the diagram illustrate an endothermic or an exothermic reaction?
Part 2: Use the labels on the diagram to describe how you can determine the total change in enthalpy from the diagram. Would you expect the value to be negative or positive?

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.