C2 The Periodic Table: Development of the Periodic Table

During the 19th Century, chemists were finding new elements almost every year, they were also finding it very hard to find patterns in which to organise the elements. 

One of the first suggestions was from John Dalton. He arranged them in elements in order of their atomic weights. In 18 08 he published his book, A New System Of Chemical Philosophy.

In 1864, John Newlands built on his idea. He found that every eighth element was similar in properties.

He produced a table showing the 'law of ocatves'.

However, he assumed all the elements had been found.

He did not take into account all of the new ones chemists were finding, so he filled his ocatves even though some were not similar at all.

Other scientists ridiculed his ideas and refused to accept them.

In 1869, Russian chemist Demitri Mendeleev cracked the problem, whereby now 50 elements had be found.  He arranged them in a table in order of their atomic weight and so that a periodic pattern would be seen in their properties.

He left gaps for the undiscovered ones. Then, he used his table to predict what their properties should be. A few years later, elements which closely resembled his prediction were discovered.

However, there are some anomalies, like Argon which has a higher relative mass than where it's put. When Mendaleev was working the Noble Gases had not been discovered. He simply changed their order to keep elements with similar properties together. 

It wasn't until the start of the 19th Century that we found out more about the structure of the atom.