Elements are arranged in groups by similay atomic structure on the periodic table. This allows for an element's properties to be predicted based on general periodic trends. Che of these trends, atomic radius, increases down a group and to the left along a period and can be defined as energy required to remove valence electron.
Explanation:
It is known that elements are grouped based on their chemical reactivity in groups of periodic tables. Along with similar chemical properties , they elements placed in a group also have similar atomic structure but they differ by their atomic radius.
So it is found that the atomic radius get increased down the group also along the left side in a period of the periodic table. Due to this atomic radius we can evaluate the energy needed to remove valence electron. As larger the element's atomic radius the lesser energy is required to remove the valence electrons from that element.
