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- The document discusses the early history and development of the periodic table, from early attempts at classification by Lavoisier and Dobereiner to the establishment of periodic law by Mendeleev. - Mendeleev arranged the elements in order of atomic mass and was able to correctly predict properties of undiscovered elements. - The modern periodic table, established by Moseley, arranges elements by atomic number rather than atomic mass, providing the foundation for studying chemistry systematically.

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SNTC SREEKANDESWARAM B.Ed. 2014 -2015
PAPER X TECNO-PEDAGOGIC CONTENT KNOWLEDGE ANALYSIS
Submitted by ARYA PRASAD PHYSICAL SCIENCE REG.NO:18214383006
Submitted to Smt.Linimol K.S Lecturer Dept. Of Physical science SNTC,Sreekandeswaram
PERIODIC TABLE
INTRODUCTION  We are living in a world full of diverse materials. Elements are the basic construction materials of all substances. At the beginning of the 19th century AD only thirty elements were known. By 1860,twice that number of elements had been discovered. Thereafter, man discovered many more elements and even synthesised some new elements. These elements have to be classified. Mendeleev succeeded in doing that by his periodic table.
ANTOINE LAVOSIERE The French Scientist Lavosiere made the first attempt to classify the elements. In 1789, he classified the 30 elements then known into metals and non-metals.
DOBEREINER’S TRIADS  . After Lavosiere ,an attempt for the classification of elements was made mainly by the German scientist Dobereiner,in AD 1829.he observed that elements can be classified into groups of three on the basis of similarities of properties. . He named them triads  In the triads, the atomic mass of the middle element is roughly the average of the atomic masses of the first and third elements. He observed such a relation in their properties also. All elements known at that time could not be grouped as triads
JOHN NEWLANDS-LAW OF OCTAVES  John Newland , an English chemist , discovered that when elements were arranged in the ascending order of their atomic masses ,each Eighth elements had similar properties as those of the first .This reminded him of the repetitive pattern of the notes of the musical octave-sa,ri,ga,ma,pa,dha,ni,sa………the eighth note being a repetition of the first.This is law of octaves.
MENDELEEV’S PERIODIC TABLE A more significant contribution to the classification of elements was made by the Russian scientist , Dmitri Ivanovich Mendeleev. It was Mendeleev’s periodic table that provided the scientific foundation for the systematic study of chemistry. After years of intense study , he established that as atomic mass increases , the properties Of elements are repeated in a periodic manner. He classified the elements on the basis of this periodic repetition and thus created the periodic table. MENDELEEV’S PERIODIC LAW • The properties of elements depend on their atomic masses When elements are arranged in ascending order of their atomic masses , it is seen that their properties are repeated at specific intervals.
MENDELEEV’S PERIODIC TABLE
MERITS  Elements having similar properties were arranged in the same groups.  The wrong atomic masses of some elements were corrected and brought them to the right place.  He predicted the properties of elements which were yet to be discovered. DEMERITS  The ascending order of the atomic masses is not strictly followed everywhere  Hydrogen was not given a proper place.  Elements having dissimilar properties were included in same groups
MODERN PERIODIC TABLE The modern periodic table , which we now use is the improved version. Moseley modified Mendeleev’s periodic law as,  properties of elements depend on their atomic numbers  When elements are arranged in the ascending of their atomic numbers there is a repetition of their properties at fixed intervals
MODERN PERIODIC TABLE
CONCLUSION New discoveries and the knowledge gained about the structure of the atoms paved the way for a detailed study of the properties of elements. The studies conducted by Moseley regarding the properties of the elements related to their position in the periodic table finally proved that the basic properties of elements depend on their atomic numbers and not on their atomic masses.
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