"The Periodic Table is arguably the most important concept in chemistry both in principle and in practice. It is the everyday supported for students, it suggests new avenues of research to professionals and it provides a succinct organization of the whole of chemistry. It is a remarkable demonstion of the fact that the chemical elements are not a random cluster of entities but instead display trends and lie together in families. An awareness of the Periodic Table is essential to anyone who wishes to disendamental the world and see how it is bult up from the fundamental building blocks of the chimestry, the chemical elements."
Glenn T.Seaborg
We know by now that the elements are the basic units of all types of matter. In 1800, only 31 elements were known. By 1865 , the number of identified elements had more than doubled to 63. At present 114 elements are known. Of them, the recently discovered elements are continuing. With such a large number of elements it is very difficult to study individually the chemistry of all these elements and their innumerable compounds individually. To ease out this problem scientists searched for a systematic way to organise their knowledge by classifying the elements. Not only that it would rationalize known chemical facts about elements but even predict new predict new once for undertaking further study.
Genesis of Periodic Classification
Classification of elements into groups and development of Periodic Law and Periodic Table are the consequences of systematising the knowledge gained by a number of scientists through their observation and experiments
The German chemist, Johann Dobereiner in early 2800'd was the first to consider the idea of trends among properties of elements. By 1829 he noted a similarly among the physical and chemical properties of serveral groups of three elements (Triads). In each case, he noticed that the middle element of each of the Trads had an atomic weight about half way between the atomic weight about half way between the atomic weight of the other two. Also the properties of the middle element were in between those of the other two members. Since Dobereiner's relationship, referred to as the Law of Triads, seemed to work only for a few elements, it was dismissed as coincidence. The next reported to classify elements was made by a French geologist, A.R.B. de Chancourtois in 1862. He arranged the then known elements in order of increasing atomic weights and made a increasing atomic weights and made a cylindrical table of elements to display the periodic recurrence of properties. This also did periodic recurrence of properties. This also did not attract much attention.
