How can the 90 or so naturally occurring elements be classified?
Are they all separate and distinct?
Do we need to learn about 90 different substances as well as some thousands of their combinations (compounds)?
Or can similar elements be studied in groups with members of each group having similar properties?
In the eighteenth century, the Swedish naturalist, Linnaeus, developed a classification system for plants and animals based on structural similarities. This was used as an argument for a Designer/Creator/God.
As the number of known elements increased during the nineteenth century, chemists looked for a similar classification system of elements by establishing relationships between them, based on their properties. In particular, the relative masses of atoms seemed to be significant.
Their efforts led to the present organisation of elements into the PERIODIC TABLE.
If you want a quick overview of the following sections, you could read this history of development of the periodic table.
Or this (on the chemistry societies network) by DrJohn Emsley which is followed by a pictorial version of the periodic table.
Or take a quick look at this periodic table site which also describes construction of a 3D version of the table, and highlights the work of Glenn Seaborg.
Atoms and elements is a set of concise lecture notes, containing photographs of Berzelius, Humphry Davy, Dalton, JJThomson, Rutherford, Newlands, Mendeleev, Bohr.
The work of Lavoisier
Dobereiner and Dumas - triads and families of four
Odling - vertical and horizontal trends
De Chantcourtois and Newlands - groupings and octaves
Meyer and Mendeleev - periodicity
Rayleigh and Ramsay - the noble gases
Moseley and Seaborg - atomic number and transuranic elements