Knowing the electron gain enthalpy values ...

NCERT Class XII Chemistry
Chapter - The p-Block Elements
Questions with Solutions

Question : 19 of 74

Marks: +1, -0

Knowing the electron gain enthalpy values for O → O– and O →O

^{2–}

as –141 and 702 kJ mol

^{–1}

respectively, how can you account for the formation of large number of oxides having O

^{2–}

species and not O

^{–}

Hint : Consider lattice energy factor in the formation of compound.

Solution:

This can be explained with the help of electronic configuration.

As O

^{2–}

has most stable configuration amongst these. So, formation of O

^{2–}

ismuch more easier. In solid state, large amount of energy (lattice enthalpy)is released to form divalent O

^{2–}

ions.It is greater lattice enthalpy of O

^{2–}

which compensates for the high energy required to remove the secondelectron.

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