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330 BCE
Aristotle
Four element theory: earth, air, fire & water -
Antoine Lavoisier
Wrote the first extensive list of elements containing 33 elements.
Distinguished between metals and non-metals. Some of Lavoisier's elements were later shown to be compounds and mixtures. -
Jöns Jakob Berzelius
Developed a table of atomic weights.
Introduced letters to symbolize elements. -
Johann Döbereiner
Forerunner to the notion of groups. 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. -
John Newlands
Forerunner to the notion of periods. 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'. Newlands' Law of Octaves identified many similarities amongst the elements, but also required similarities where none existed. He did not leave spaces for elements as yet undiscovered. -
Lothar Meyer
Compiled a Periodic Table of 56 elements based on the periodicity of properties such as molar volume when arranged in order of atomic weight. -
Dmitri Mendeleev
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 (the elements were gallium, scandium and germanium). The order of elements was re-arranged if their properties dictated it. This enabled the properties of elements to be predicted properties of the elements vary periodically with their atomic weights. -
William Ramsay
Discovered four gases (neon, argon, krypton, xenon) and showed that they (with helium and radon) formed an entire family of new elements, the noble gases. -
Henry Moseley
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. Moseley's modified Periodic Law puts the elements tellerium and iodine in the right order, as it does for argon and potassium, cobalt and nickel. -
Glenn Seaborg
Synthesised transuranic elements (the elements after uranium in the periodic table). These new elements were part of a new block of the Periodic table called Actinides. Seaborg was awarded a Nobel Prize in 1951.
