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ICSE Class X Notes 2021 : Chemistry (Periodic Classification of Elements)

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Bharati Gulajkar
Lokhandwala Foundation School (LFS), Kandivali East, Mumbai
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CHAPTER 5 Periodic Classification of Elements I n Class IX we have learnt that matter around us is present in the form of elements, compounds and mixtures and the elements contain atoms of only one type. Do you know how many elements are known till date? At present, 118 elements are known to us. All these have different properties. Out of these 118, only 94 are naturally occurring. As different elements were being discovered, scientists gathered more and more information about the properties of these elements. They found it difficult to organise all that was known about the elements. They started looking for some pattern in their properties, on the basis of which they could study such a large number of elements with ease. 5.1 MAKING ORDER OUT OF CHA Y EARLY CHAOS OS EARL ATION OF ASSIFICA ATT THE CL ASSIFIC ATTEMPTS A ELEMENTS We have been learning how various things or living beings can be classified on the basis of their properties. Even in other situations, we come across instances of organisation based on some properties. For example, in a shop, soaps are kept together at one place while biscuits are kept together elsewhere. Even among soaps, bathing soaps are stacked separately from washing soaps. Similarly, scientists made several attempts to classify elements according to their properties and obtain an orderly arrangement out of chaos. The earliest attempt to classify the elements resulted in grouping the then known elements as metals and non-metals. Later further classifications were tried out as our knowledge of elements and their properties increased. 5.1.1 D bereiner s Triads Figure 5.1 Imagine you and your friends have found pieces of an old map to reach a treasure. Would it be easy or chaotic to find the way to the treasure? Similar chaos was there in Chemistry as elements were known but there was no clue as to how to classify and study about them. In the year 1817, Johann Wolfgang D bereiner, a German chemist, tried to arrange the elements with similar properties into groups. He identified some groups having three elements each. So he called these groups triads . D bereiner showed that when the three elements in a 2020-21

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