(i) Ionisation energy:- It is the amount of energy required to remove an electron from an isolated gaseous atom.

(ii) Electron affinity:- Electron affinity is the energy which is released when an extra electron is added to an isolated gaseous atom in its outermost shell.

(iii) Atomic radii:- The distance from the center of the nucleus to the outermost shell is defined as atomic radii.

(iv) Modern periodic law:- Properties of the element are a periodic function of their atomic number.