The history of the periodic table and its elements can be traced as far back as Ancient Greek times. They believed in four simple elements. These were: earth, air, water, and fire. This idea of elements was never picked up again until the 17th and 18th centuries. Also, another Greek idea was that the universe was made out of small particles called atoms. Leucippus and Demokritos had the idea of that and worked together. However, Aristotle (a Greek philosopher) disagreed, and the idea never carried on. Then, about 200 years ago, a man named John Dalton suggested the same thing. He did continuous research, like combining a hydrogen atom with an oxygen atom to form water.
Evidence like this paved the way for the theory, and his Atomic Theory was eventually accepted. Back to the elements, though… Antoine Lavoisier drew up a table of 33 of them for his book ‘Traitï¿½ Elï¿½mentaire de Chimie’ (Elementary Treatise of Chemistry), published in 1789. Lavoisier grouped them into four categories based on their chemical properties: gases, non-metals, metals and earth. In the early 1800s, all the chemists could go on was Relative Atomic Mass and physical and chemical properties. They had no idea about the atomic structure of protons and electrons. This meant there was no ‘proton number’ to them. So far, the discovered elements were arranged in order of atomic mass only, and so obviously, things were bound to be wrong.
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Johnann Doebereiner used this method and arranged the elements also by their properties. He discovered that barium, calcium and strontium had similar properties and arranged them in a group of three – a triad. This continued as more triads were being put together. In 1863 – 1864, John Newlands arranged the elements, again in order of atomic masses. The only difference was that Newlands wanted to expand upon Doebereiner’s idea and relate each element to the other. He noticed that every eighth element had similar properties and listed the known elements in rows of seven. Unfortunately, this broke down on the third row because the transition metals confused the whole table. He also left no gaps in his table.
In 1869, in Russia, Dmitri Mendeleev expanded upon Newland’s table. His idea was that there must have been more than the discovered 50 or so elements, so he decided to arrange them by atomic mass but leaving gaps to fit new elements in. When new elements were found, they fitted in nicely. However, after this adjustment, he still had two elements that did not fit. Those elements were tellurium and iodine. Mendeleev assumed that the masses had been mismeasured, and he placed them according to property. The table had a few other inconsistencies that were discovered as this table was used. Nevertheless, Mendeleev is known as the Father of the Modern Periodic Table.
In 1913 Henry Moseley conducted X-ray experiments on elements. The outcome of his experiments led to the discovery of the atomic number. He announced that if Mendeleev had arranged his table by atomic number instead of atomic mass, the little inconsistencies would not have occurred. He led this on to the blueprint of the modern periodic table. Unfortunately, he did not continue his work as he died whilst being out at war.