Dmitri Mendeleev, a Russian chemist, is renowned for developing the first widely recognized periodic table in $1869$. His groundbreaking approach involved organizing the elements primarily by their atomic weight, which is the total mass of protons and neutrons in an atom. However, Mendeleev’s methodology extended beyond just atomic weight; he also considered the chemical properties of the elements, grouping those with similar traits together.

Mendeleev’s periodic table was more than a mere list of elements; it was structured in a grid-like format, with elements arranged in rows and columns. The horizontal rows, known as periods, represented different energy levels of the atoms, while the vertical columns, referred to as groups, contained elements with analogous properties. This systematic arrangement enabled Mendeleev to illustrate the periodicity of the elements, showcasing the repeating patterns in their characteristics.

One of the most impressive features of Mendeleev’s periodic table was his ability to predict the existence of yet-to-be-discovered elements. He intentionally left gaps in his table, where he anticipated new elements would fit based on the patterns he observed. Furthermore, he predicted the properties of these unknown elements. Remarkably, when these elements were eventually discovered and their properties measured, Mendeleev’s predictions proved to be highly accurate.

Over the years, Mendeleev’s periodic table has undergone significant refinement and expansion. The modern periodic table is now arranged by atomic number (the number of protons in an atom), rather than atomic weight. Nonetheless, the fundamental principles of Mendeleev’s arrangement—grouping elements by similar properties and recognizing periodicity—continue to underpin the structure of the periodic table today.