What is the general trend in first ionization energy as we move down a column (group) in the periodic table?

• A. It first increases, then decreases
• B. It decreases
• C. It remains constant
• D. It increases

Answer: (B)

Verified step by step guidance

1. Understand that first ionization energy is the energy required to remove the outermost electron from a neutral atom in the gaseous state.
2. Recognize that as you move down a group in the periodic table, atoms have more electron shells, increasing the distance between the nucleus and the outermost electron.
3. Consider that increased distance and additional inner electron shells cause greater electron shielding, which reduces the effective nuclear charge felt by the outermost electron.
4. Since the outermost electron is held less tightly due to increased shielding and distance, less energy is required to remove it, meaning the first ionization energy decreases.
5. Therefore, the general trend is that first ionization energy decreases as you move down a column (group) in the periodic table.