Question

The correct order of electron gain enthalpy (magnitude only) for group 16 elements is:

• A. \( \mathrm{Te>Se>S>O} \)
• B. \( \mathrm{S>Se>Te>O} \)
• C. \( \mathrm{O>S>Se>Te} \)
• D. \( \mathrm{S>O>Se>Te} \)

Hint:

Remember:
Oxygen has lower electron gain enthalpy than sulfur due to strong inter-electronic repulsion.
Always check for exceptions involving small atoms like O and F.

Answer 1

The Correct Option is B

Concept: Electron gain enthalpy is the enthalpy change when an electron is added to a neutral gaseous atom. Since the values are generally negative, magnitude only means we compare how strongly atoms attract an extra electron, ignoring the sign. Key factors affecting electron gain enthalpy:
Atomic size
Effective nuclear charge
Electron--electron repulsion in small orbitals
Step 1: Trend in group 16 elements. Group 16 elements are: \[ \mathrm{O,\ S,\ Se,\ Te} \] On moving down the group:
Atomic size increases
Electron gain enthalpy generally becomes less negative However, oxygen is an exception due to its very small size.
Step 2: Comparing oxygen with sulfur. Oxygen has a very small \(2p\) orbital. When an extra electron enters, there is strong electron--electron repulsion, which reduces its tendency to gain an electron. Sulfur has a larger \(3p\) orbital, so it can accommodate an extra electron more easily. Hence: \[ \mathrm{S>O} \]
Step 3: Comparing sulfur, selenium, and tellurium. As we move down from sulfur to selenium to tellurium:
Atomic size increases
Attraction for incoming electron decreases Therefore: \[ \mathrm{S>Se>Te} \]
Step 4: Final order (magnitude only). Combining all comparisons: \[ \mathrm{S>Se>Te>O} \] \[ \boxed{\mathrm{S>Se>Te>O}} \]