Question

In which of the following, elements are arranged in the correct order of their electron gain enthalpies?

• A. \(F\gt S\gt O\gt N\)
• B. \(F\gt O\gt S\gt N\)
• C. \(F\gt O\gt N\gt S\)
• D. \(F\gt N\gt O\gt S\)

Hint:

Elements with stable half-filled or completely filled configurations have lower electron gain enthalpy. Also, smaller atoms like oxygen may show lower electron gain enthalpy due to electron-electron repulsion.

Answer 1

The Correct Option is A

Step 1: Understand electron gain enthalpy.
Electron gain enthalpy is the energy released when an isolated gaseous atom gains an electron.
More negative electron gain enthalpy means greater tendency to accept an electron.

Step 2: Compare the given elements.

Fluorine (F):
Fluorine has very high effective nuclear charge and strong attraction for an incoming electron. Hence, it has very high electron gain enthalpy.

Sulphur (S) and Oxygen (O):
Although oxygen is above sulphur in the group, oxygen has a very small atomic size. Due to greater electron-electron repulsion in compact \(2p\)-orbitals, oxygen has less negative electron gain enthalpy than sulphur.
Thus, \[ S\gt O \]

Nitrogen (N):
Nitrogen has half-filled stable configuration: \[ 1s^22s^22p^3 \] Adding one electron disturbs this stable arrangement, so nitrogen has very low electron gain enthalpy.
Hence, \[ N \] has the least tendency to gain an electron among the given elements.

Step 3: Arrange in decreasing order.
Therefore, the correct order is \[ F\gt S\gt O\gt N \]

Step 4: Final conclusion.
Hence, the correct arrangement is \[ \boxed{F\gt S\gt O\gt N} \]