As you move from left to right across a period in the periodic table, what happens to the ionization energy of the elements?

• A. Ionization energy first increases, then decreases.
• B. Ionization energy remains constant.
• C. Ionization energy decreases.
• D. Ionization energy increases.

Answer: (D)

Verified step by step guidance

1. Understand that ionization energy is the energy required to remove an electron from a gaseous atom or ion.
2. Recall that as you move from left to right across a period in the periodic table, the number of protons in the nucleus increases, which increases the effective nuclear charge experienced by the electrons.
3. Recognize that the increased effective nuclear charge pulls the electrons closer to the nucleus, making them more tightly bound and harder to remove.
4. Therefore, the ionization energy generally increases across a period because more energy is needed to remove an electron from an atom with a stronger nuclear attraction.
5. Note that this trend can have small exceptions due to electron configurations, but the overall pattern is an increase in ionization energy from left to right across a period.