The first classification of elements was as metals and non-metals. This served only limited purpose mainly because of two reasons:

1. All the elements were grouped in to these two classes only. Moreover the group containing metals was very big.

2. Some elements showed properties of both-metals and non-metals and they could not be placed in any of the two classes.

After this, scientists made attempts to recognize some pattern or regularity in variation of properties of elements and to classify them accordingly. Now we shall learn about some of them.