Why does ionization energy tend to decrease from top to bottom within a group on the periodic table?

• A. Because electron shielding decreases, making it easier to remove an electron.
• B. Because atoms gain more electrons in their outermost shell, increasing their ionization energy.
• C. Because atomic radius increases, causing the outer electrons to be farther from the nucleus and less tightly held.
• D. Because the number of protons decreases, reducing the nuclear charge.

Answer: (C)

Verified step by step guidance

1. Understand that ionization energy is the energy required to remove an electron from an atom in its gaseous state.
2. Recognize that as you move down a group in the periodic table, atoms have more electron shells, which increases the atomic radius.
3. Know that a larger atomic radius means the outermost electrons are farther from the nucleus, so the electrostatic attraction between the nucleus and these electrons is weaker.
4. Consider the effect of electron shielding, where inner electrons partially block the attraction between the nucleus and the outermost electrons, making it easier to remove an electron.
5. Conclude that because of the increased distance and shielding, ionization energy decreases from top to bottom within a group.