Periodic Table — Periodic Properties & Variation of Properties — Question 14

Reasons for Periodicity in properties in periods and groups is as follows —

1. After definite intervals of atomic number, similar valence shell electronic configuration occurs i.e., same number of electrons are present in the outermost orbit of the elements.
2. Properties of elements depend upon the number and arrangement of electrons in various shells including valence shells.
3. In the same period or sub-group, increase or decrease in a particular property is due to gradual change in electronic configuration in the arranged elements.