Periodic Table - Dmitri Mendeleev Essay

526 WordsApr 17, 20123 Pages
During the ancient times in Greece there once was a very well known philosopher named Aristotle. Aristotle thought that there were only four elements used in science and they were Earth, Water, Air and Fire. Scientists knew that there were more than four elements. Scientists began a long search for what substances are made of, but as scientific techniques advanced so did the unknown elements. As more elements were discovered scientists looked for ways to organise them. Then the French chemist Antoine-Laurent de levier separated the known elements into metals, non-metals and earths. Soon after in 1808 John Dalton, an English chemist, went further by giving each of the 36 elements its own chemical symbols and organising in order of their mass. Then came along Dmitri Mendeleev, he created the same periodic table we use till today. Mendeleev realized 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. Gaps and predictions 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 to be right. For example, he predicted the properties of an undiscovered element that should fit below aluminium in his table. When this element, called gallium, was discovered in 1875 its properties were found to be close to Mendeleev's predictions. Two other predicted elements were later discovered, lending further credit to Mendeleev's table. It is also important to notice how the

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