In 1869, Mendeleev created the Periodic Table, or as he called it, the Periodic System. When he was created the Periodic Table, only 60 elements had been discovered (in comparison to the 100+ we know of today).
Mendeleev wrote the properties of the elements on cards and organized them in order of increasing atomic weight. For example, a reactive non-metal was directly followed by a very reactive light metal, then a less reactive light metal.
His periodic tabled looked like this
Mendeleev wrote the properties of the elements on cards and organized them in order of increasing atomic weight. For example, a reactive non-metal was directly followed by a very reactive light metal, then a less reactive light metal.
His periodic tabled looked like this
or
Mendeleev is considered to be the "father" of the Periodic Table because he put elements in their correct places in the table, since he corrected the miscalculated relative atomic mass by other scientists. Additionally, Mendeleev decided that some atomic weights must be incorrect because the element appeared in the wrong place. Today, we know that the placement of elements in the periodic table are positioned by their atomic number (reference the atomic number page for more information), not by their atomic mass (reference the atomic mass page for more information).