Chemistry PERIODIC CLASSIFICATION OF ELEMENTS Part-1
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Periodic Classification

The arrangement of elements in such a way so that elements having similar properties reappear at a regular interval, is called periodic classification or periodic arrangement of elements.

Earlier Development in Classification of Elements

Several attempts have been made for the classification of elements into group and it leads to the development of periodic classification and periodic table of elements.

Dobereiner's Triads

Dobereiner (1817) found that elements could be arranged in a group of three elements called triads in such a way that the middle element had an atomic weight almost the average of other two. e.g.
Element Li Na K
Atomic weight 7 23 39
Mean of atomic masses ` = (7+39)/2 = 23`

Newlands' Law of Octaves

John A.R. Newland (1866) found that, if the elements were arranged in the increasing order of their atomic weights, the properties of every eighth elements were similar to those of first one. Newland called it law of octaves.

Lothar Meyer's Arrangement of Elements

Lothar Meyer (l865) plotted various physical properties such as atomic volume against atomic weight and said "the properties of the elements were the periodic functions of their atomic volumes." He arranged the elements in a way resembling Mendeleev's arrangement of elements.

 
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