Which of the following have the most negative electron gain enthalpy ?

Question

Accepted Answer

The correct answer to the question is Option 2: Cl. Here is a detailed explanation supporting why chlorine (Cl) has the most negative electron gain enthalpy, along with reasons why the other options are incorrect:

1. **Explanation for Option 2 (Cl):**
   - Chlorine has the most negative electron gain enthalpy among the given options. Electron gain enthalpy is the energy change that occurs when an electron is added to a neutral atom in the gaseous state to form a negative ion. A more negative value indicates a greater tendency to gain an electron.
   - Chlorine is in Group 17 of the periodic table, known as the halogens. Halogens have high electron affinities because they are one electron short of having a complete octet, which makes them highly eager to gain an electron.
   - Among the halogens, chlorine has a more negative electron gain enthalpy than fluorine due to its larger atomic size, which reduces electron-electron repulsion in the added electron's orbital. This makes the addition of an electron more energetically favorable for chlorine than for fluorine.

2. **Explanation for why other options are incorrect:**

- **Option 1 (F):**
     - While fluorine is also a halogen and has a high electron affinity, its electron gain enthalpy is less negative than that of chlorine. This is because fluorine's small atomic size leads to significant electron-electron repulsion when an additional electron is added, making the process slightly less favorable compared to chlorine.

- **Option 3 (P):**
     - Phosphorus is in Group 15 of the periodic table and does not have as high an electron affinity as the halogens. Its electron gain enthalpy is less negative because it is not as energetically favorable for phosphorus to gain an electron compared to chlorine, which is closer to achieving a stable octet.

- **Option 4 (S):**
     - Sulfur, like phosphorus, is also in Group 16, but it does not have as high an electron affinity as chlorine. While sulfur does have a relatively high electron affinity, it is still less negative than that of chlorine due to the differences in atomic structure and the energy changes involved in gaining an electron.

In conclusion, chlorine (Cl) has the most negative electron gain enthalpy among the given options due to its position in the periodic table and its atomic properties, making it the correct answer.