SNTC SREEKANDESWARAM B.Ed. 2014 -2015

PAPER X TECNO-PEDAGOGIC CONTENT KNOWLEDGE ANALYSIS

Submitted byARYA PRASAD PHYSICAL SCIENCE REG.NO:18214383006

Submitted toSmt.Linimol K.SLecturerDept. Of Physical scienceSNTC,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. DRAWBACK 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 TABLEA 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.