Question

How does ionization energy change down a group?

Answer 1

Ionization energy is the measure of the difficulty in removing the electron from the atom. The trend of ionization energy in the periodic table is related to the atomic radius and the principle quantum number. As we move down in the group, more electron shells are added and as a result the outermost electrons become distant from the nucleus.

Complete step by step answer:
The ionization energy is defined as the measure of the difficulty in removing an electron from an atom or ion. It is also defined as the tendency of the atom or ion to surrender an electron.
In other words, ionization energy is described as the measure of the strength by which the electrons are held in their place.
The electrons present in the valence shell can be easily removed as they are present in the outermost orbit of the atom.
In the periodic table, as we move down in the group more energy levels are added and as a result the valence electrons move further away from the positive nucleus. This results in the attraction between the Valence electrons and nucleus to decrease. This decrease in attraction is known as shielding effect.
The less is the attraction between the valence electrons and the nucleus, the more easier the electrons are removed.
The ionization energy increases on moving from left to right in the period as the atomic radius decreases and the ionization energy decreases on moving top to bottom in the group. This is due to the increase in the principal quantum number of the outermost electron increases down in the group.

Note:
When the ionization energy is high, it will be more difficult to remove the electrons. Ionization energy depends on the strength of the attraction between the negative electron and the positive nucleus.