It is a table that classifies all the known elements in accordance with their properties in such a way that elements with similar properties are grouped together in the same vertical column and dissimilar elements are separated.
The 115 known elements are arranged in the Periodic Table in order of their increasing atomic number. The vertical columns are called groups. The horizontal rows are called periods.
It is based upon the modern periodic law, i.e. elements are arranged according to the increasing order of their atomic number.