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Johann Dobereiner's 'Triads'
In 1829, Johann Dobereiner came up with the idea of organising the elements into groups of three called 'Triads'. Each Triad had a certain set of chemical and physical properties - eg. Chlorine, Bromine and Iodine, which are all in Group 7 of the modern Periodic Table. -
John Newlands and the 'Law of Octaves'
John Newlands realised that if the various elements were arranged by atomic weight, then certain properties were repeated every eight elements. He likened this to the octaves on a piano's keyboard. This idea was widely ridiculed by the established scientists of the day, and also did not work beyond the element calcium. -
Dmitri Mendeleev invents the idea of a Periodic Table
Dmitri Mendeleev, a Russian from Siberia, published a table of elements in which the elements were organised into 'groups' vertically, and by atomic weight into 'periods' horizontally. These periods each contained eight elements. -
Lothar Meyer's table
At the same time, Lothar Meyer published a table of elements orgainising them by their atomic weights. However, Mendeleev believed that if the established atomic weight of a certain element did not fit into his table, then it must have been wrong. He thus corrected the atomic weights of Beryllium, Indium, and Uranium. -
Mendeleev predicts three elements
Mendeleev also predicted the discoveries of three elements in later years - Scandium, Gallium, and Germanium. These were discovered over the next twenty years, and let to wide acceptance of his theories. -
Henry Mosely discovers atomic weights
Henry Mosely, while working with X-rays, discovered that each element had a specific atomic number, relating to the positive charges in the nucleus. However, he was killed soon after, during the invasion of Gallipoli. -
Glenn T. Seaborg
After helping with the discoveries of ten elements, Glenn Seaborg decided to move fourteen more out of the main body of the table. These became the actinide series, and were placed underneath the Lanthanides.
