In the 1800's, scientists had no idea about the structure of atoms, but they could measure the relative atomic mass of each element.
When all the elements were put in order of their relative atomic mass, scientists began to notice periodic patterns in the properties of elements.
Dmitri Mendeleev arranged the elements in groups
He arranged 50 or so known elements according to their properties and the properties of their compounds to make a table of elements.
Mendeleev's table placed elements with similar…