Before the nineteenth century, only a few elements were known. These elements could

be easily studied individually.

With the passage of time, many more elements were discovered. More and more of

their compounds were prepared. Study of these elements and compounds individually

became more difficult. So, it was felt that these elements should be classified into a

few groups to make their study systematic and easier. It is expected that a systematic

classification will help us in

• organising the knowledge,

• predicting new elements for undertaking further studies.

One of the earliest attempts towards the classification of elements was to divide these

into metals, and non-metals.

This method of classification failed because most of the elements fell into the

category of metals, whereas only a few elements could be grouped as non-metals.

There were also a few elements which showed the properties of both metals and

non-metals.

Since then, many attempts were made by various scientists to classify elements

in a more systematic way. A few important attempts for the classification of

elements are described over here. There are more than one hundred chemical elements

known today. It is very difficult to study the properties of each element individually, so

these elements were classified on the basis of their similarities in properties. In this

course, we shall discuss the historical development of Mendeleev's periodic table,

modern periodic law and the electronic configuration of atoms as the basis for periodic

classification, the characteristics of s, p, d, f block elements and the periodicity

in physical and chemical properties of the elements.