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Which of the following pairs of elements would have more negative electron gain enthalpy? (i) O or F (ii) F or CI. |
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Answer» Solution :(i) O or F. Both O and Flie in 2nd period. As we move from O to F the atomic size decreases. Due to smaller size of F nuclear charge increases. Further, gain of ONE electron by `FtoF^(-)` F-ion has inert gas configuration, While the gain of one electron by `OtoO^(-)` GIVES `O^(-)` ion which does not have stable inert gas configuration. Consequently, the energy RELEASED is much higher in going from `FtoF^(-)` than going from `OtoO^(-)`. In other words electron gain enthalpy of F is much more negative than that of oxygen. (ii) The negative electron gain enthalpy of Cl(eg. `DeltaH= -349 KJ mol^(-1)`) is more than that of F(eg. `DeltaH= - 328 kJ mol^(-1)`). The reason for the deviation is due to the smaller size of F. Due to its small size, the electron repulsions in the relatively compact 2p-subshell are comparatively large and hence the attraction for incoming electron is less as in the case of Cl. |
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