Discovery of the Periodic Table

In the 1800s the periodic tables were organized into one physical and one chemical characteristics of elements. Chemist, Dimitri Mendeleev, organized the periodic table using the average atomic mass of each element. Another criterion used was the "combining capacity" of the elements. The table was formed in vertical and horizontal columns. The vertical columns had elements with similar chemical properties and the horizontal columns had the elements in increasing atomic masses. Now, the elements in the leftmost column are very reactive metals and the rightmost column are unreactive gases.