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The development of the periodic table began in the 19th century. Johan Döbereiner.
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The development of the periodic table began in the 19th century. Johan Döbereiner attempted to classify the elements by their atomic weight. He identified 'triads', three elements with similar properties, such as chlorine, bromine and iodine. The element in the middle, bromine would have an atomic weight which would be the average of chlorine and iodine. Cl - 35 Br - 80 I - 127 (127+35)/2 = 81 An illustration of the triad theory (1) John Newlands then introduced the Law of Octaves, stating that every eighth element in the table had similar properties. However, in 1869, Russian Dimitri Mendeleev created a new version by finding correct atomic weight values. He left gaps for undiscovered elements which he predicted the finding of. This attempt was different to earlier ones as Döbereiner attempted to classify elements along with two other ones in triads and John Newlands tried to group the elements he discovered in...
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