Quantization: means that a quantity does not vary continuously. The energy of an electron in an atom cannot have any arbitrary value but only certain characteristic values. ­A definite quantum of energy is accepted while moving from lower to higher energy level or lost while moving from higher to lower energy level, It does not accept any amount of energy nor does it lose energy continuously.

Quantum of energy related to:
1 – frequency
2 – wavelength of the radiation emitted or absorbed
E = hυ            E= hc/λ
where h =Planck's constant, υ=Frequency of radiation and c= velocity of light