CBSE Class 10 Science Chapter 5 - Periodic Classification of Elements
Brief Information: In Standard 9 we have learned that matter around us is present in the form of elements, compounds and mixtures and the elements contain atoms of only one type. The early attempts at the classification of elements resulted in grouping the then-known elements as metals and non-metals. Dobereiner grouped the elements into triads and Newlands gave the Law of Octaves. Mandelvee arranged the elements in increasing order of their atomic masses and according to their chemical properties. He even predicted the existence of some yet to be discovered elements on the basis of gaps in his Periodic table. The modern periodic table came into existence. Mendeleev’s Periodic Law was modified and the atomic number was adopted as the basis of the Modern Periodic Table and the Modern Periodic Law can be stated as follows: ‘Properties of elements are a periodic function of their atomic number’.
In this chapter, Periodic Classification of Elements, elements in the Modern Periodic Table are arranged in 18 vertical columns called groups and 7 horizontal rows called periods. Elements thus arranged show periodicity of properties including atomic size, valency or combining capacity and metallic and non-metallic character. The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom. The term atomic size refers to the radius of an atom.
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