In 1869, Dmitri Mendeleev created the periodic table of elements, which organizes the known elements by increasing atomic number. The periodic table is still used today as a powerful tool for organizing, understanding, and predicting the properties of atoms and the elements they form.
Mendeleev's original periodic table was based on the repeating patterns of properties he observed in the elements. He placed elements with similar properties in the same column, which he called "groups." The modern periodic table is organized in a slightly different way, but it still includes Mendeleev's original grouping of elements.
The periodic table is a powerful tool for chemists because it allows them to predict the properties of new elements, as well as the compounds those elements will form.