SATHEE: Classification of Elements and Periodicity in Properties

Classification of Elements and Periodicity in Properties - Result Question 13

####13. The formation of the oxide ion $O^{2 -} (g)$ , from oxygen atom requires first an exothermic and then an endothermic step as shown below : $O (g) + e^{-} \to O^{-} (g); Δ_{f} H^{⊖} = - 141 k J m o l^{- 1}$ $O^{-} (g) + e^{-} \to O^{2 -} (g); Δ_{f} H^{⊖} = + 780 k J m o l^{- 1}$ 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

(d) Addition of electron in oxygen results in larger size of the ion.

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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.

Classification of Elements and Periodicity in Properties - Result Question 13

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Classification of Elements and Periodicity in Properties - Result Question 13

Solution:

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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