(a) What is the trend in first ionization energies as one proceeds down the group 17 elements? Explain how this trend relates to the variation in atomic radii. (b) What is the trend in first ionization energies as one moves across the fourth period from K to Kr? How does this trend compare with the trend in atomic radii?

Verified step by step guidance

1. Step 1: Understand the concept of first ionization energy, which is the energy required to remove the outermost electron from a neutral atom in the gaseous state.
2. Step 2: For part (a), identify the trend in first ionization energies as you move down Group 17 (halogens) in the periodic table. Note that ionization energy generally decreases down a group.
3. Step 3: Explain that as you move down Group 17, atomic radii increase due to the addition of electron shells, which results in the outermost electrons being further from the nucleus and less tightly held, thus requiring less energy to remove.
4. Step 4: For part (b), identify the trend in first ionization energies as you move across the fourth period from potassium (K) to krypton (Kr). Note that ionization energy generally increases across a period.
5. Step 5: Explain that as you move across a period, atomic radii decrease due to increased nuclear charge pulling electrons closer, which results in electrons being more tightly held and requiring more energy to remove.