He had predicted the existence of elements with atomic numbers 23, 31 and 32, and what properties they should exhibit. There should have been a certain element with that atomic number, and should have some predictable properties, but they had not yet been discovered. In some cases, this left empty positions in the periodic table. Mendeleev, who introduced the concept, gave an atomic number to each known element. These are known as the atomic numbers of the elements. Tellurium went into position 52 and iodine into 53. For example, tellurium has a higher atomic mass than iodine, but Mendeleev placed it before iodine, so that each element would be placed directly below another element with similar properties. While most of the elements were indeed arranged according to their atomic weights, some elements did not follow the rule of periodicity. He chose to rely more on chemical properties instead. In 1869, when Dmitri Ivanovich Mendeleev, a Russian chemist, created the periodic table, he chose not to arrange the elements exactly according to their atomic weights. When the next element would have similar properties with an earlier element, it would be entered in the net row, but below the earlier element in the same column.ĪLSO READ | Explained: What Is Chandrayaan-3? ISRO's Moon Mission Set To Launch In July To Analyse The Lunar Surface How it was created
A certain number of elements, each with different properties, would be ordered in a row. Therefore, it was possible to group these elements into columns. In other words, the chemical properties of an element would be repeated, or be largely similar, in another element after a certain number of entries. In the 19th century, scientists had found that if they arranged the elements in the order of their atomic masses, the properties of the elements showed a “periodicity”. In the periodic table, elements are arranged in a certain order.
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