Why does the ionization energy decrease in a column?

Answer 1

Ionisation energy increases across a period and decreases down a group. This could be explained on the basis of their nuclear charge and atomic radii. As you move across a period, the nuclear charge goes on increasing and it becomes increasingly difficult to remove the outermost electron.

As you move across a period, the atomic radii goes on decreasing. This implies that the valence electrons are strongly attracted by the nucleus. Hence it becomes difficult to remove the outermost loosely bound valence electron.

Therefore, inonisation energy increases as we move across a period.

Answer 2

The ionization energy decreases in a column because the atomic size increases as you move down the column, resulting in a weaker attraction between the outer electrons and the nucleus. This weaker attraction makes it easier to remove an electron, leading to a lower ionization energy.