Final answer:
Ionization energy generally increases with increasing effective nuclear charge, as the nucleus's attraction to valence electrons becomes stronger, requiring more energy to remove an electron.
Step-by-step explanation:
Ionization energy (IE) tends to increase with increasing effective nuclear charge (Zeff). The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. This takes into account the shielding effect of other electrons which tends to reduce the full nuclear charge experienced by an electron.
The trend in ionization energy can be observed in the periodic table. As you move across the periodic table from left to right (as →PT, IE ↑), the number of protons in the nucleus increases, enhancing the effective nuclear charge. Consequently, the attraction between the nucleus and the valence electrons grows stronger, requiring more energy to remove an electron, which leads to an increase in ionization energy.
However, as we go down a group in the periodic table (as↓ PT), the ionization energy decreases because the valence electrons are increasingly farther from the nucleus due to added electron shells, which reduces the effect of the nuclear charge.