The element with highest electron affinity in the periodic table is?

A. Iodine

B. Chlorine

C. Fluorine

D. Oxygen

The element with the highest electron affinity in the periodic table is Chlorine (B). While Fluorine is often thought to have a higher electron affinity due to its high electronegativity, Chlorine actually has a more negative electron affinity value when measured. Let’s break this down further to understand why this is the case.

Understanding Electron Affinity

Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gas phase. A more negative value indicates a greater tendency to gain an electron. The trend in electron affinity can be influenced by several factors, including atomic size and the effective nuclear charge.

Trends in the Periodic Table

• Group Trends: As you move down a group in the periodic table, electron affinity generally decreases. This is because the added electron is further from the nucleus, experiencing less attraction.
• Period Trends: Across a period from left to right, electron affinity tends to increase. This is due to the increasing nuclear charge, which attracts electrons more strongly.

Comparing the Elements

Now, let’s examine the options provided:

• Iodine (I): Being lower in the periodic table, iodine has a lower electron affinity compared to chlorine.
• Chlorine (Cl): Chlorine has an electron affinity of about -349 kJ/mol, which is more negative than that of fluorine.
• Fluorine (F): Fluorine has a high electron affinity of about -328 kJ/mol. Although it is highly electronegative, the small size of fluorine leads to electron-electron repulsion when an additional electron is added, slightly reducing its electron affinity.
• Oxygen (O): Oxygen has an electron affinity of about -141 kJ/mol, which is significantly lower than both chlorine and fluorine.

Why Chlorine Wins

The reason Chlorine has the highest electron affinity lies in its balance of size and nuclear charge. Chlorine is larger than fluorine, which allows the added electron to be added more easily without the significant repulsion that occurs in fluorine. Thus, while fluorine is very electronegative, chlorine's electron affinity is more favorable when considering the energy released upon gaining an electron.

Final Thoughts

In summary, while it might be tempting to think that fluorine, being the most electronegative element, would have the highest electron affinity, chlorine actually takes the lead. This is a great example of how periodic trends can sometimes lead to surprising conclusions. So, the correct answer to your question is B. Chlorine.