Chem 3 - Development of the Periodic Table - The early Periodic Table

At the start of the 1800's, scsientists didn't know much about atoms, didn't have a complete list of the elements, and each chemical compounds had numerous names. They would try and find patterns and similarities between the elements they found, in order to try and organise them somehow.

One of the first suggestions was from a man named John Dalton. He arranged the elements in order of their mass, measured in various chemical reactions.

A man named John Newlands built on Daltons ideas with his law of octaves. Newlands based this idea on the fact that the properties of every 8th element seemed similar. He produced a table based on this, but was so determined for it to work that he made several vital mistakes:

- He assumed that all of the elements had been found, and so filled in the table regardless of the fact that some elements weren't similar at all.

- He even put 2 elements in the same place at the some points to make everything fit in.

In 1869, the Russian scientist Dmitri Mendeleev crack the problem. At this time, 50 elements had been identified. Mendeleev arranged all of these in a table. He placed all of them in order of their atomic masses. Then he arranged them so that a periodic pattern in their physical and chemical properties could be seen.

His stroke of genius was to leave gaps for elements that had not yet been discovered. But he predicted what their properties should be from his table. A few years later, new elements were discovered with properties which matched almost exactly Mendeleev's predictions.