The History of the Periodic Table

By the time John Dalton proposed his Atomic Theory in 1808 there were about 30 known elements. By about 1860 there were around 60 elements. Dalton originally thought that the elements were unrelated. However, as more elements were discovered and there physical and chemical properties investigated relationships began to emerge.

A German named Dobereiner saw that there was a triad relationship between some of the elements. If the elements with similar properties were arranged in groups of three in order of increasing atomic mass, like chlorine, bromine and iodine patterns could be seen. If the atomic mass of the first and third triad was average it was very close to the atomic mass of the second element.

John Newlands latter proposed the law of octaves in that every 8 elements is a kind of repetetion of the first of the eight elements.

Dmitri Mendeleev systemicatically gathered date on the known 63 elements known at his time in 1869 and arranged in the elements in groups with similar properitesand in order of increasing atomic weight. His work formed the basis of the modern Periodic Table with a modification that today, the elements are arranged according to increasing Atomic number.