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Which of the following pairs of elements would have more negative electron gain enthalpy? 1. O or F 2. F or Cl. |
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Answer» 1. O or F. Both O and F lie in 2e” period. As we move from O to F the atomic size decreases. Due to smaller size off nuclear charge increases. Further, gain of one electron by F → F- F- ion has inert gas configuration, While the gain of one electron by O → O- gives O ion which does not have stable inert gas configuration. Consequently, the energy released is much higher in going from F → F- than going from O → O- . In other words electron gain enthalpy off is much more negative than that of oxygen.- 2. The negative electron gain enthalpy of Cl (e.g. ∆H = – 349 mol-1) is more than that of F (e.g. ∆H = -328 U mol-1 ). The reason for the deviation is due to the smaller size off. Due to its small size, the electron repulsion 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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