Need for Classification of Elements
Before the beginning of the eighteenth century, only a few elements were known, so it was quite easy to study and remember the properties of those elements and their compounds individually. However, by the middle of the nineteenth century, more than sixty elements had been discovered.
The number of compounds formed by them was also enormous. With the increasing number of elements, it was becoming more and more difficult to study their properties individually. Therefore, the need for their classification was felt. This led to the classifications of various elements into groups which helped in the systematic study of elements.
Development of Classification
Scientists after many attempts were successful in arranging various elements into groups. They realised that even though every element is different from others, yet there are a few similarities among some elements. Accordingly, similar elements were arranged into groups which led to classification.
Various types of classification were proposed by different scientists. The first classification of elements was into 2 groups - metals and non-metals. This classification served only limited purpose mainly because some elements like germanium and antimony showed the properties of both metals and non-metals. They could not be placed in any of the two classes.
Scientists were in search of such characteristics of an element which would never change. After the work of William Prout in 1815, it was found that the atomic mass of an element remains constant, so it could form the basis for a satisfactory classification. Four major attempts were made for classification of elements. They are:
- Dobereiner's Triads
- Newlands' Law of Octaves
- Mendeleev's Periodic Law & Periodic Tables
- Modern Periodic Table