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Earlier Attempts On Classification Of Elements


Posted Date: 12-Aug-2011  Last Updated:   Category: Education    
Author: Member Level: Gold    Points: 12


Modern science world is knowing information about more than 114 elements and have a periodic table prepared by Henry Moseley which makes the study more easy. But before the appearance of the modern periodic table there was many attempts that deserve respect. This resource is a brief write up about those attempts and their main principles. This resource is help for plus one students of Kerala state syllabus as it is related to third chapter in Chemistry.



Earlier attempts of classification of Elements

Johann Dobereiner Triad model

The first attempt on classification of elements have no definite proof as early man started to classify elements based on his needs. But a scientific method of classification was first introduced by the German chemist Johann Dobereiner in 1829. He classified the elements to groups of three. It should be noticed that there was only less number of elements at that time and many were not discovered. A classification method at that time therefore really deserve appreciation. Dobereiner thus created a law based on his classification and was called Law of Triads.
The name triads came as his classification included elements in a group of three. He also noticed that there was relation in the classified group. The middle element, ie, the second element was having somewhat an atomic mass which was equal to the average mass of other two elements in the group. This was the basis of Law of Triads.

A.E.B. de Chancourtois Table of elements

When the Law of Triads lost its importance due to practical problems second classification method was made by the French chemist in 1862. This classification was also not able to cause attention.It was a miserable failure. Still his name is not that famous for this work. But this method later lead to many other important discoveries of classification. So it really deserve respect as any others.
The criteria used by the scientist was on the basis of atomic weights. He tried to classify the elements that were known at that time in the increasing order of atomic weights. He also prepared a cylindrical table to show the periodicity of elemental properties. But unfortunately all ended up in failure.

John Alexander Newlands octave structure

In 1865 the English chemist, Newlands came with more proof for the periodic structure of elements.
He classified available elements into a group of 8 and created Law of Octaves based on his observance of the classification. The observance led to an interesting feature of the table that was prepared by Newlands.
In the group of 8, the last element showed properties of first element and this periodicity was just like the notes of music ( Sa, Ree, etc.). When Newlands noticed this periodical repeating nature he defined the law of Octaves. The anxious matter was the basis of classification.Newlands also took increasing order of atomic weights for his classification. But this model was not accepted universally.

Dmitri Mendeleev and Lothar Mayer,s periodic table

After the long list of classifications the works of this two scientists caused an impact on scientific world. Both came up with same work but Mendeleev was the one with dominance. These 2 personalities are given great respect in chemical world for their contributions. They worked independently and was working on the same method of classification. Dmitri Mendeleev, the German chemist was the first to publish. So the credit goes to him. The basis of their classification was increasing order of atomic weights itself. The difference was the consideration of other physical properties like melting point etc. Mendeleev published the his Law in 1869 and was followed for long time.
Mendeleev's periodic law
The properties of elements are periodic functions of their atomic weights.
But this model also had its own limitations. Still all respect the hard work behind the classification method. Later this classification model which had 8 groups was replaced by modern table with 18 groups prepared by Moseley.


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