Question

what is the basis for arranging elements in modern periodic table

Answer 1

Elements are arranged according to increasing atomic number in periods (rows) and groups (columns) such that elements that have similarities in chemical behaviour and atomic structure are arranged in the same groups.

Answer 2

The major characteristic, besides the number of protons, is the outer shell of electrons. For example, the left-most column has a single electron in that shell, and these atoms tend to combine with those toward the far right of the periodic table (not the noble gases), but those needing an electron or two to complete their outer shells.