Periodic Table History

The periodic table is one of the most important icons that consolidates much of our knowledge about chemistry. For over 200 years, the table has recorded the elements and classifying as best as it could. Since elements were be discovered, scientists often improved and changed the table. The term "periodic" reflects how the events show patterns in their properties. When they discovered this, they put elements with similar properties in groups or families.

On February 17, 1869, a Russian professor named Dimitri Mendeleev completed and made the first periodic table.

He arranged the elements according to increasing atomic weight. Because he did this, he could predict some undiscovered elements. Mendeleev was not the only one that was developing a system to describe the elements. Other scientists have tried but was not very successful as Mendeleev.

Johann Döbereiner pointed out that elements could be arranged in groups of three that he called triads. He also added that the middle elements is close to the average of the weights for the first and third members of the triad. Döbereiner's work encouraged others to search for correlations between the chemical properties of the elements and atomic weight.

The crucial characteristic about Mendeleev's system was that it illustrated a periodicity, or repetition. Several other scientists tried to find ways to group the elements such as John Newlands. He suggested that when elements were arranged in order of atomic weight, any one of the elements showed properties similar to those of the element eight places ahead and eight places behind in the list. He called the feature "the law of octaves."

During the time Mendeleev spent making his own periodic table, a chemist named Julius Lothar Meyer from Germany was in the process of revising a textbook when he produced a table very similar to Mendeleev's famous 1869 version. The table did not appear until 1870 due to the printers delay. Lothar Meyer had trouble classifying the elements correctly and since Mendeleev's table had a predictive aspect was a major advance.