Which of the following best describes the periodic trends in electron affinity across the periodic table?

• A. Electron affinity increases both across a period and down a group.
• B. Electron affinity generally increases across a period from left to right and decreases down a group.
• C. Electron affinity generally decreases across a period from left to right and increases down a group.
• D. Electron affinity remains constant across periods and groups.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand what electron affinity means. Electron affinity is the amount of energy released or absorbed when an atom gains an electron. It reflects how strongly an atom attracts additional electrons.
2. Step 2: Analyze the trend across a period (left to right). As you move from left to right across a period, atoms have more protons in the nucleus, increasing the nuclear charge. This stronger attraction generally causes atoms to release more energy when gaining an electron, so electron affinity increases.
3. Step 3: Analyze the trend down a group (top to bottom). Moving down a group, atoms have more electron shells, which increases the distance between the nucleus and the added electron. This reduces the effective nuclear attraction due to shielding, so electron affinity generally decreases.
4. Step 4: Summarize the overall trend. Electron affinity generally increases across a period from left to right because of increasing nuclear charge and decreases down a group because of increased electron shielding and distance.
5. Step 5: Apply this understanding to the answer choices. The correct description matches the trend where electron affinity increases across a period and decreases down a group.