How does ionization energy change down a group?

Question

Luna Chen · Accepted Answer

Ionization energy generally decreases down a group.

Ionization energy is the energy needed to remove one electron from an atom in the gaseous state.

This electron would be a valence electron, or an electron in the outermost energy level/shell, because they're the easiest to remove.

Ionization energy depends mainly on the strength of the attraction between the negative electron and the positive nucleus.

When we move down a group in the periodic table, more energy levels are added, and so valence electrons would become further and further away from the positive nucleus.

This causes the attraction between valence electrons and the nucleus to decrease, something known as the shielding effect.

The less attraction between the electrons and the nucleus, the easier they are to remove—decreasing ionization energy.

Ellie Andrews · Answer

undefined Ionization energy generally decreases down a group in the periodic table. This trend is due to the increasing atomic radius and the higher number of electron shells as one moves down a group. These factors cause the outermost electrons to be farther from the nucleus, resulting in a weaker attraction between the nucleus and the outermost electron. Consequently, less energy is required to remove an outer electron from an atom, leading to lower ionization energy as you move down a group.