Question

The electron gain enthalpy (in kJ/mol) of oxygen, sulphur, selenium respectively are

• A. \(-195, -200, -141\)
• B. \(-195, -141, -200\)
• C. \(-141, -200, -195\)
• D. \(-141, -195, -200\)

Hint:

Electron gain enthalpy becomes less negative down the group, except for sulfur, which has a more negative value than oxygen due to better electron accommodation.

Answer 1

The Correct Option is C

Step 1: Understanding Electron Gain Enthalpy
- Electron gain enthalpy (\(\Delta H_{\text{eg}}\)) is the energy released when an atom gains an electron.
- Moving down a group, electron gain enthalpy generally becomes less negative due to increasing atomic size and decreasing nuclear attraction. Step 2: Comparing the Elements
- Oxygen (O, atomic number 8): \( \Delta H_{\text{eg}} = -141 \, \text{kJ/mol} \)
- Sulfur (S, atomic number 16): \( \Delta H_{\text{eg}} = -200 \, \text{kJ/mol} \)
- Selenium (Se, atomic number 34): \( \Delta H_{\text{eg}} = -195 \, \text{kJ/mol} \) Step 3: Observing Trends
- Sulfur has the most negative value because of better electron accommodation compared to oxygen.
- Selenium has a slightly less negative value than sulfur due to its larger size.
- Oxygen has the least negative value due to increased electron repulsion in its small \(2p\) orbital. Thus, the correct order is: \[ \mathbf{O (-141), S (-200), Se (-195)} \] Thus, the correct answer is \( \mathbf{(3)} \ -141, -200, -195 \).