The Early Periodic Table
An English scientist called John Newlands put forward his Law of Octaves in 1864. He arranged all the elements known at the time into a table in order of relative atomic mass. When he did this, he found a pattern among the early elements. The pattern showed that each element was similar to the element eight places ahead of it.
For example, starting at Li (lithium), Be (beryllium) is the second element, B (boron) is the third and Na (sodium) is the eighth element. He then put the similar elements into vertical columns, known as groups.
Newlands' table showed a repeating or periodic pattern of properties, but this pattern eventually broke down. By ordering strictly according to atomic mass, Newlands was forced to put some elements into groups which did not match their chemical properties.
For example, he put iron (Fe), which is a metal, in the same group as oxygen (0) and sulfur (S), which are two non-metals.
As a result, his table was not accepted by other scientists.
In 1869, just five years after John Newlands put forward his Law of Octaves, a Russian chemist called Dmitri Mendeleev published a periodic table. Mendeleev also arranged the elements known at the time in order of relative atomic mass, but he did some other things that made his table much more successful.
He realised that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
Sometimes this method of arranging elements meant there were gaps in his horizontal rows or 'periods'. But instead of seeing this as a problem, Mendeleev thought it simply meant that the elements which belonged in the gaps had not yet been discovered.
He was also able to work out the atomic mass of the missing elements, and so predict their properties. And when they were discovered, Mendeleev turned out...