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ISC Class XI Notes 2019 : Chemistry (Classification of Elements and Periodicity)

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Chemistry (www.tiwariacademy.com) (Chapter 3) (Classification of Elements and Periodicity) (Class XI) Question 3.1: What is the basic theme of organisation in the periodic table? Answer 1.1: The basic theme of organisation of elements in the periodic table is to classify the elements in periods and groups according to their properties. This arrangement makes the study of elements and their compounds simple and systematic. In the periodic table, elements with similar properties are placed in the same group. Question 3.2: Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that? Answer 3.2: Mendeleev arranged the elements in his periodic table ordered by atomic weight or mass. He arranged the elements in periods and groups in order of their increasing atomic weight. He placed the elements with similar properties in the same group. However, he did not stick to this arrangement for long. He found out that if the elements were arranged strictly in order of their increasing atomic weights, then some elements did not fit within this scheme of classification. Therefore, he ignored the order of atomic weights in some cases. For example, the atomic weight of iodine is lower than that of tellurium. Still Mendeleev placed tellurium (in Group VI) before iodine (in Group VII) simply because iodine s properties are so similar tofluorine, chlorine, and bromine. 1 www.tiwariacademy.com

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