Kaplan Nursing Entrance Practice Exam 2025 – The All-in-One Guide to Exam Success!

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. As you move across a period from left to right on the periodic table, several changes occur that influence ionization energy.

One key factor is the increase in nuclear charge, meaning that the number of protons in the nucleus increases with each successive element. This heightened nuclear charge results in a greater attractive force between the positively charged nucleus and the negatively charged electrons. Consequently, the electrons are held more tightly, which increases the energy needed to remove one of them — thus raising the ionization energy.

Another factor is the decrease in atomic radius as you move from left to right across a period. With more protons in the nucleus, the electrons are drawn closer, reducing the distance between the nucleus and the outermost electron. This proximity further amplifies the attraction, contributing to the increase in ionization energy.

This trend of increasing ionization energy across a period is consistent across the periodic table, as observed in various elements. Understanding the interplay of nuclear charge and atomic radius helps clarify why ionization energy consistently escalates in this direction.