A long time ago, scientists studied the elements Potassium, Sodium and Lithium and found that they all react alike with water, oxygen and chlorine to produce similar compounds. It had been shown that lithium has a lower rate of reaction than sodium, whereas potassium has a higher rate of reaction than sodium. When you link this with their atomic masses, sodium is yet again the middle element! This same pattern is repeated with other groups of threes, for example: Bromine, Iodine and Chlorine, which eventually became known as the Law of Triads. The Law of Triads was discovered in early 1817 by Johann Dobereiner who was a German Chemist. This was the beginning of looking for trends in the arrangements of elements, though at the time this law was considered only as a little curiosity considering only a few elements and their masses were known.
About fifty years later, John Newlands, an English chemist, discovered a new method for organising the elements and by this time lots of new elements had been discovered and had been measured much more accurately. He took Dobereiner’s simple ideas involving similar properties and improved them, by relating all the elements to each other to find a certain pattern. He found out that after intervals of eight, similar physical or chemical properties reappeared again in the element, so he decided to write a paper regarding this explaining his “Law of Octaves”.
Dmitri Mendeleev is a Russian Chemist who devised the periodic table we know to this very day. He took some of Newlands’ ideas and improved on them, to devise his own table, which was quite similar to Newlands’. He decided it would be a good idea to leave gaps in his table so that in the future, elements that are yet to be discovered could be placed neatly into those gaps. Over the last 140 year, all of these elements have been discovered! After doing so, he was able to predict the properties of a new element using the properties of the other elements in that group. Now, the elements are arranged in order of increasing atomic number.
This Periodic Table was improved again in 1895 when a completely new group was introduced for the noble gases as previously none had been discovered. Physicist Lord John Rayleigh discovered a new gas called Argon which was chemically inert and therefore didn’t fit into any of the periodic groups. A British chemist called Sir William Ramsay also happened to discover Helium, Neon and Krypton, so he positioned these gases on the right hand side of the periodic table, and they are now known as the Noble Gases.
The most recent version of the periodic table is based upon Moseley’s Periodic Law, regarding atomic numbers. Another major change that occurred was when Glenn Seaborg discovered some of the lanthanide and actinide elements, numbers from 94 to 102, and decided to modify the periodic table by placing these elements at the bottom of the table.
The periodic table is made up of vertical groups and horizontal periods. In the vertical groups, elements have the same number of the electrons in their outer shell, and in horizontal periods, elements have the same principal quantum.
Many scientists have put in a lot of work to form the periodic table that we use to this very day. As technology progresses and our understanding gets better, this periodic table could even develop further in years to come!
