Elements may have similar properties and we can use the periodic table to us determine what they are. these three elements are alike in many ways but they do not share all properties. what property do these elements not have in common?

same number of valence electrons

Explanation:

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.