Mendeleev arranged the periodic table in order of increasing atomic weight of the elements. He determined that there was a pattern when he arranged these elements into horizontal rows.
Mendeleev placed the elements into horizontal rows in his periodic table of elements. He recognized a distinct pattern when he did this but only when he left some blanks in between certain elements. The pattern that he noticed was that certain chemical properties showed up at regular, periodic intervals in the vertical columns of the table.
Because there were blanks left in the table after it was arranged how Mendeleev wanted it to be, he predicted that there were many elements that had not yet been discovered. His periodic table received some controversy from other scientists for this reason. However, only a few years later there were more discoveries of elements being made. The periodic table provided the template for classification of elements by their chemical properties and atomic weight. It made it necessary to determine these details before classifying.
Mendeleev created his chart between the years of 1868 and 1870 as he was writing his book titled "The Principles of Chemistry." Although he is credited for the basic outline of the periodic table of elements, there were several scientists who came after him in completing the periodic table that exists today. Scientists brought about national pride for discovering elements.