Which of the following statements correctly describes periodic trends in ionization energy?

• A. Ionization energy generally decreases across a period from left to right.
• B. Ionization energy remains constant as you move down a group.
• C. Ionization energy generally increases across a period from left to right.
• D. Ionization energy increases as you move down a group.

Answer: (C)

Verified step by step guidance

1. Recall that ionization energy is the energy required to remove an electron from an atom in its gaseous state.
2. Understand the trend across a period (left to right): As you move across a period, the nuclear charge increases while the electron shielding remains relatively constant, causing electrons to be held more tightly.
3. Therefore, ionization energy generally increases across a period from left to right because the effective nuclear charge increases, making it harder to remove an electron.
4. Consider the trend down a group (top to bottom): As you move down a group, the atomic radius increases due to the addition of electron shells, which increases electron shielding.
5. Thus, ionization energy generally decreases down a group because the outer electrons are farther from the nucleus and are held less tightly, making them easier to remove.