What the ultimate Natural Units of material are?
What is a chemical element?

Periodic Tables of Chemical Elements

Discovered more chemical elements after Lavoisier
Dobereiner notice some triads (three elements with similar properties)
Mendeleyev (1834-1907) and Meyor (1830-1895) independently organized property information about chemical elements. Their effort resulted in periodic tables of elements
Mendeleyev made a bigger impact because his tables predicted the existence of some elements unknown at that time.
Since arrangements according to atomic weight were unsatisfactory, atomic numbers were invented
Periodic tables guided the search of new elements, served as a framework showing the relationship among elements, confirmed a substance as an element, and steered the synthesis of new elements