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Four element theory: earth, air, fire & water. Aristotle could only see Water, Earth, Fire, and Air.
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Wrote the first extensive list of elements containing 33 elements.
Distinguished between metals and non-metals. -
Developed 'triads', groups of 3 elements with similar properties.
Lithium, sodium & potassium formed a triad.
Calcium, strontium & barium formed a triad.
Chlorine, bromine & iodine formed a triad. -
The known elements (>60) were arranged in order of atomic weights and observed similarities between the first and ninth elements, the second and tenth elements etc. He proposed the 'Law of Octaves'.
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Compiled a Periodic Table of 56 elements based on the periodicity of properties such as molar volume when arranged in order of atomic weight.
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Produced a table based on atomic weights but arranged 'periodically' with elements with similar properties under each other. Gaps were left for elements that were unknown at that time and their properties predicted
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Determined the atomic number of each of the elements.
He modified the 'Periodic Law' to read that the properties of the elements vary periodically with their atomic numbers.
