modern periodic table

Introduction

In the early nineteenth century about 30 elements were known and were classified into three types on the basis of their physical properties as: metals, nonmetals and metalloids. Subsequent noteworthy attempts For classification of the increasing number of elements based on atomic mass were Dobereiner's triads and Newlands' octaves.

Development of periodic table

Dobereiner's triads :

In this arrangement, three elements having similar properties were placed in a group so that the atomic weight of the middle element was average of atomic weights of remaining two elements. 
Mendeleev's periodic table : The elements were arranged in the increasing order of their atomic weights, in the horizontal rows or periods and the elements having similar properties were kept in the same group. Hence this periodic table consisted of nine groups (0 to VIII) and eleven periods. Vacant places were left for the undiscovered elements which were filled later on.
 After the discovery of atomic structure, the atomic number, which was an ordinary number assigned to element in Mendeleev's periodic table, was recognize proton number, Z, of that element. This was the outcome of Henry Moseley's work on x-ray spectroscopic study of a large number of elements. 

Modern periodic table or Long form of the periodic table :

This periodic table was developed with a principle that the chemical and physical  properties of the elements are periodic functions of their atomic  numbers. This periodic table consists of 18 groups and 7 periods, elements are divided in four series namely s, p, d and f series  according to their electronic configuration. The elements in the same group have the same properties f-block elements namely 4f-series | Lanthanoids 5f-series (Actinoids] are kept separately below the periodic table.