Saturday, June 18, 2011

Significance of Mendeleef’s Periodic Table

Some of the important uses of Mendeleef’s periodic table are as follows:-

(I).   Prediction of New Elements

At the time of Mendeleef only 63 elements were known and on arranging these elements in periodic table keeping in mind the similarity in properties of elements, certain vacant places were left which provided a clue for the discovery of new elements. For example, both Gallium and Germanium were not discovered at that time when Mendeleef proposed periodic table. So gaps were left below Aluminium and Silicon. Mendeleef named these elements as Eka –Aluminium Eka –Silicon respectively which would fill the gap in future. Mendeleef also predicted their properties and later on, when these elements were discovered, the properties predicted by Mendeleef proved remarkably correct.

(II). Determination of Correct Atomic Masses & Valency

With the help of Mendeleef’s periodic table doubtful atomic masses as well as valencies of certain elements were corrected. For exampleBeryllium was assigned an atomic mass 13.5. On the basis of equivalent mass (4.5) and valency (calculated as 3). Therefore, Beryllium with atomic mass 13.5 should been placed between carbon (At. Mass – 12) and nitrogen (At. Mass –14). But there was no place vacant between carbon and nitrogen and moreover the properties of Beryllium did not justify such position. Hence valency two was assigned to Beryllium which gave it the atomic mass equal to 9 (At. Mass = Eq. Mass ´Valency). So, it was placed at its proper place between Lithium (At. Mass-7) and Boron (At. mass-11).

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