Many individuals contributed to the development of the periodic table.
Johann Dobereiner (1817): Dobereiner noticed that several elements could be grouped in such a way that the properties of one element in each group was the average of the other two elements in the group. These groups of three elements were called triads. The relationship between the three elements in each group was called the Law of Triads.
A. E. Beguyer de Chancourtois (1862): De Chancourtois constructed a cyliinder with the known elements arranged such that sixteen mass units were written on the cylinder per turn. He noticed that this caused closely related elements to line up on the cylinder. De Chancourtois was the first to recognize that many element properties repeated every seven elements.
John Newlands (1863): Newlands classified the known elements into groups based on similar physical properties. He noticed that many pairs of similar elements had atomic weights that differed by a multiple of eight. This was called the Law of Octaves.
John Meyer (1864): Meyer constructed a partial periodic table with the elements listed in order of their atomic weight. In 1968, he constructed a more complete periodic table very similar to Mendeleevs (see below).
Dmitri Mendeleev (1870): Mendeleev created a card for each of the known elements. Each card showed the element symbol, atomic weight, and the element's properties. He then arranged the cards in order of increasing atomic weight, while grouping cards with similar properties together. Based on his arrangement of elements, Mendeleev was able to predict the properties of elements that had not yet been discovered.
Henry Moseley (1913): Moseley's research into the spectral lines of elements led to the realization that the properties of the elements varied with atomic number, rather than atomic mass. This led to the ordering of the periodic table by atomic number instead of atomic mass.
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