Could anybody please explain me the concept of ionization energy in the elements of the periodic table??

IONIZATION ENERGY: The energy is required to remove the electron from the neutral atom is called ionization energy. In periodic the ionization energy is decreases from top to bottom of the periodic table in the groups. Because the new shells are formed in groups and therefore the distance between the nucleus and outermost valance shell is increases.Therefor ionization energy is decreases. In periods the ionization energy is neither increases nor decreases, it is vary in the periods.Because of in the periods there are few elements have half filled electronic configuration. -------------Please excuse me if the mistakes are appear.