<human>:  What is the history of the periodic table?
<bot>: The history of the periodic table begins in the early 19th century, when scientists recognized that elements could be arranged based on their similarities. In 1869, the Russian chemist Dmitri Mendeleev created the first periodic table, which arranged elements in order of increasing atomic mass and grouped them according to their chemical and physical properties. This breakthrough provided a way to systematize the properties of elements and opened the door to multiple discoveries, including the existence of previously unknown elements. Over the next 140 years, new elements were discovered, atomic numbers assigned, and new elements added to the table. In 2012, four new elements were added, completing the seventh row of the periodic table and bringing the total number of elements to 118.