Elements, Acids and Bases

In the Early 1800's
Only categorised the elements in two ways:
1) their physical and chemical properties
2) their relative atomic mass

They had no idea of atomic structure or of protons or electrons, so there was no such thing as atomic number to them. In the 1800's the only thing that they could do was measure the relative atomic mass, and so the known elements were arranged in order of atomic mass. When this was done a periodic pattern was noticed.

Newlands' Law of Octaves
In 1864 Newlands tried to rearrange the elements. He noticed that every eigth element had similar properties, so he listed the elements in rows of seven:

H  Li  Be  B  C  N  O 
F  Na