Wrote the first extensive list of elements containing 33 elements. He also distinguished between metals and non-metals.
Developed a table of atomic weights and introduced letters to symbolise elements
Developed 'triads', groups of three elements with similar properties. Lithium, Potassium and Sodium formed a triad, Calcium, Strontium and Barium formed a triad, and Chlorine, Bromine, and Iodine formed a triad.
The known elements (less than 60) were arranged in order of atomic weights. He also observed similarities between the first and ninth elements, the second and tenth elements, etc. He proposed the Law of Octaves.
Compiled a Periodic Table of 56 elements based on the periodicity of properties such as molar volume when arranged in order of atomic weight.
Produced a table based on atomic weights but arranged it 'periodically' with elements with similar properties under each other. Gaps were left for elements that were undiscovered at the time and their properties were predicted. The order of elements were rearranged if their properties dictated it.