Why does fluorine have a higher ionization energy than iodine?

• A. Iodine has more protons, which increases its ionization energy.
• B. Fluorine has a smaller atomic radius, so its valence electrons are held more tightly by the nucleus.
• C. Fluorine has more electron shells, which increases shielding and lowers ionization energy.
• D. Iodine is more electronegative, so it holds its electrons more tightly.

Answer: (B)

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 ionization energy depends on the effective nuclear charge (the net positive charge experienced by valence electrons) and the distance of the valence electrons from the nucleus.
3. Note that fluorine has fewer electron shells than iodine, meaning its valence electrons are closer to the nucleus and experience less shielding from inner electrons.
4. Because fluorine's valence electrons are held more tightly due to a smaller atomic radius and higher effective nuclear charge per electron, it requires more energy to remove an electron compared to iodine.
5. Understand that although iodine has more protons, the increased number of electron shells causes greater shielding, reducing the effective nuclear charge felt by its valence electrons and thus lowering its ionization energy.