Question

The increasing order of electron gain enthalpy of the following substances is:

$O<S<Se<Te$

If the order of bond dissociation enthalpy is correct, enter 1 else 0.

Answer 1

Electron gain enthalpy is the amount of energy released when an element accepts an electron. The process is endothermic.

$\text{Lesser the electronic repulsion faced by an electron to get occupied in the outermost shell higher the amount of}$

$\text{energy released.}$

On moving down the group, the electron gain enthalpy decreases from S to Po. Oxygen has an unexpectedly low value of electron gain enthalpy.

Since oxygen is smaller in size than S, so incoming $e^{-}$ on oxygen faces more electronic repulsion on oxygen outermost surface ( due to more $e^{-}$ density) as a result electron affinity decreases.

The increasing order of electron gain enthalpy with negative sign is

$O(-141.4kJ/mol)<Po(-174kJ/mol)<Te(-190.0kJ/mol)<Se(-195.5kJ/mol)<S(-208.8kJ/mol)$

Hence the correct answer is 0.