Classification Of Elements And Periodicity In Properties Ques 5
5. The formation of the oxide ion $O^{2-}(g)$, from oxygen atom requires first an exothermic and then an endothermic step as shown below : $O(g)+e^{-} \to O^{-}(g) ; \Delta_f H^{\ominus}=-141 kJ mol^{-1}$ $O^{-}(g)+e^{-} \to O^{2-}(g) ; \Delta_f H^{\ominus}=+780 kJ mol^{-1}$
Thus process of formation of $O^{2-}$ in gas phase is unfavourable even though $O^{2-}$ is isoelectronic with neon. It is due to the fact that [2015 RS]
(a) Electron repulsion outweighs the stability gained by achieving noble gas configuration
(b) $O^{-}$ion has comparatively smaller size than oxygen atom
(c) Oxygen is more electronegative
(d) Addition of electron in oxygen results in larger size of the ion.
Show Answer
Answer:
Correct Answer: 5.(a)
Solution:
(a) Incoming electrons occupies the smaller $n$ $=2$ shell, also negative charge on oxygen $(O^{-})$is another factor due to which incoming electron feel repulsion.
Hence, electron repulsion outweigh the stability gained by achieving noble gas configuration.
BETA
