The Periodic Table

As the number of known elements

As the number of known elements increased, classification became necessary to study them in an organised way and to relate one element with another. A

J

J. W. Dobereiner grouped elements into sets of three called triads. The middle element had an atomic mass approximately equal to the average of the ot

Dobereiner's law did not arrange all

Dobereiner's law did not arrange all known elements into triads and did not fully work even within the same family. The halogen example fluorine, chlo

John Newland arranged elements in increasing

John Newland arranged elements in increasing atomic mass and observed that every eighth element had properties similar to the first. This was called t

The law worked well only

The law worked well only for lighter elements. It failed for heavier elements and placed some very different elements in the same column. It also coul