Question

The correct order of magnitude of electron gain enthalpy of $O,S$ and $Se$ is:

• A. O > S > Se
• B. S > O > Se
• C. S > Se > O
• D. O > Se > S

Answer 1

The correct option is B S > Se > O

Moving down across a group 16, we have, O, S, Se, and then Te.

We know that as we move down a group, the electron gain enthalpy decreases so the trend should be O > S > Se > Te.

But the elements of period 2 generally have less electron gain enthalpy because they have a smaller, more compact size which leads to electron repulsion with the incoming electrons.

Thus, as oxygen is in period 2, it will have less electron gain enthalpy than all the other

chalcogens.
Hence, The correct order of magnitude of electron gain enthalpy is S > Se > O