Ionization energy (IE) is the energy required to remove the highest-energy electron from a neutral atom. In general, ionization energy increases across a period and decreases down a group. ... Down a group, the number of energy levels (n) increase and the distance is greater between the nucleus and highest-energy electron.

Does ionization energy decreases down the group?

On the periodic table, first ionization energy generally decreases as you move down a group. This is because the outermost electron is, on average, farther from the nucleus, meaning it is held less tightly and requires less energy to remove.

Does ionization energy increase up a group?

The ionization energy of the elements increases as one moves up a given group because the electrons are held in lower-energy orbitals, closer to the nucleus and thus more tightly bound (harder to remove).