Justify the statement, bigger size atoms have more shielding effect thus low ionization energy
Answer: Bigger size atoms have more shielding and low ionization energy: Shielding effect is the decrease in attractive forces between the nucleus and outer electrons. Shielding effect increase with the increase of size of the atoms.
It is because that with the addition of more inner shells and inner electrons the attractive forces between nucleus and outer electrons decreases. It means that the electrons present in the filled energy levels screen or shield the attraction of nucleus felt by the valence shell electrons. This shielding effect increases from top to bottom in a group because of increase in size of atom.
On the other hand Ionization energy which is the energy required to remove loosely bound electron from the valence shell of an isolated gaseous atom decreases with the increase of size and increase in shielding effect. because of decreases in effective nuclear charge, electron removal becomes easy.
In a period the shielding effect decreases from left to right. Because of same number of inner electrons and increase in valence shell electrons and protons in the nucleus. This causes an increase in the effective nuclear charge and thus size of atoms decreases. Due to small size, low screening effect and high effective charge, the electron removal becomes difficult and thus ionization energy increases.