Which of the following best describes the relationship between atomic radius and ionization energy across a period in the periodic table?

• A. There is no relationship between atomic radius and ionization energy.
• B. As atomic radius increases, ionization energy decreases.
• C. Atomic radius and ionization energy both increase together.
• D. As atomic radius decreases, ionization energy increases.

Answer: (D)

Verified step by step guidance

1. Understand the definitions: Atomic radius is the distance from the nucleus to the outermost electron in an atom, while ionization energy is the energy required to remove an electron from a gaseous atom or ion.
2. Recall the trend across a period (left to right) in the periodic table: As you move across a period, the atomic number increases, meaning more protons in the nucleus, which increases the effective nuclear charge.
3. Because the effective nuclear charge increases, electrons are pulled closer to the nucleus, causing the atomic radius to decrease across a period.
4. With electrons held more tightly due to the increased nuclear charge and smaller radius, it requires more energy to remove an electron, so ionization energy increases across a period.
5. Therefore, the relationship is that as atomic radius decreases, ionization energy increases across a period in the periodic table.