Saved Bookmarks
| 1. |
Which of thefollowingpairs of elementswouldhave anegativeelectrongainenthalpy ? (i)O or F(ii) F or Cl |
|
Answer» Solution :(i) bothO andf liein 2ndperiod . As wemovefrom O to F ,the ATOMICSIZEDECREASES and thenuclearcharge increases .Boththesefactorstendto increase the ATTRACTIONS of thenucleusfor theincomingelectron and henceelectrongain ethalpy becomesmorenegative , Further, gain ofone electronby F gives `F^(-)` ion whichhas stableinertgasconfigurationwhilethe gainof oneelectronby Ogives `O^(-)` ion whichdoesnot have stableinertgasconfiguration, Consequently the energy released is muchhigherin goingfromf `to F^(-)` than ingoingfrom `O to O^(-)` ,Inotherwordselectron gainenthalpyof F ismuchmorenegative (- 328 KJ `mol^(-1)`)than THATOF oxygen`(-141 kJ mol^(-1))` (ii)In general the electrongain enthalpy becomesless negativeon movingdown thegroup. Buttheelectrongainenthalpy of chlorine`(-349 kJ mol^(-1))` is morenegativethan thatof flurine(-328 kJ `mol^(-1)`). Thereasonfor thisdeviationis thesmallsizeof F atom. Dueto itssmall size theelectron electron repulsionsin therelatively compact 2p- subshellare comparativelylargeand hencethe incomingelectronis notacceptedwith thesameease as isthe case withlarge C1 atom.Consequentlyelectron gainenthalpy of C1 is morenegativethan thatof F. |
|