Question

Identify the element having positive electron gain enthalpy.

• A. Ne
• B. I
• C. S
• D. O

Hint:

Noble gases have positive electron gain enthalpy due to their stable electron configuration.

Answer 1

The Correct Option is A

Concept:
Electron gain enthalpy is the enthalpy change when an isolated gaseous atom gains an electron: \[ X(g)+e^- \rightarrow X^-(g) \]

• Negative value $\Rightarrow$ energy released, electron accepted easily
• Positive value $\Rightarrow$ energy absorbed, electron addition difficult

Step 1: General periodic trend
Most non-metals have negative electron gain enthalpy because they tend to gain electrons. Noble gases usually have positive electron gain enthalpy because their outer shell is completely filled and very stable.
Step 2: Check each option

• Ne (Neon): Noble gas with stable octet configuration
• I (Iodine): Halogen, readily gains electron
• S (Sulfur): Non-metal, gains electron easily
• O (Oxygen): Non-metal, tends to gain electron

Step 3: Reason for Neon
Neon has electronic configuration: \[ 1s^2\,2s^2\,2p^6 \] Its valence shell is complete. Adding an electron would require entry into the next higher shell, which needs energy. \[ \Rightarrow \text{Positive electron gain enthalpy} \]
Step 4: Final Answer
The element having positive electron gain enthalpy is: \[ \boxed{\text{Ne \] Quick Tip:
Noble gases usually have positive electron gain enthalpy because of highly stable filled shells.