Which element has the highest electron affinity (most negative value)?

• A. O
• B. Cl
• C. Br
• D. F

Answer: (B)

Verified step by step guidance

1. Understand that electron affinity is the energy change that occurs when an atom gains an electron, typically measured in kJ/mol. A more negative value means the atom releases more energy and has a higher tendency to accept an electron.
2. Recall the general trend of electron affinity in the periodic table: it tends to increase (become more negative) across a period from left to right and decrease (become less negative) down a group.
3. Compare the elements given: Oxygen (O), Fluorine (F), Chlorine (Cl), and Bromine (Br). All are in Group 16 or 17, with O and F in period 2, Cl and Br in periods 3 and 4 respectively.
4. Note that although Fluorine is more electronegative, its electron affinity is less negative than Chlorine's due to electron-electron repulsions in the small 2p orbital. Chlorine, being larger, can better accommodate the extra electron, resulting in a more negative electron affinity.
5. Conclude that among the given elements, Chlorine (Cl) has the highest (most negative) electron affinity based on periodic trends and atomic structure considerations.