Question

How many of the following elements have negative
value of first electron gain enthalpy?
H, Li, Na, K, Rb, Cs, O, S, Se, Te, Po, He, Xe,
Kr. Br. At​

Answer 1

given elements are ; H , Li , Na K, Rb , Rb , Cs O , Se , Te , Po , He, Xe , Kr , Br, At

We have to check which has negative electron gain enthalpy.

solution : electron gain enthalpy is the amount of heat released when we add one electron in an isolated gaseous atom.

For half filled and completely filled outermost orbit, electron gain enthalpy will be positive because it has require heat to add electron.

Here, He, Xe and Kr are noble gases so these have completely filled outermost orbits. So electron gain enthalpies for these are always positive.

Now rest elements have negative because

(H , Li , Na K, Rb , Cs ) belongs to 1st group ( ns¹) so we can easily add one electron.

(O, S, Se , Te , Po) belongs to oxygen family (np² ) so adding of electron, gives negative electron gain enthalpy.

And Br and At (Astatine) elements belomg to halogen family, have also negative electron gain enthalpies.

So there are 13 elements which have negative electron gain enthalpies

Answer 2

Answer :-

given elements are ; H , Li , Na K, Rb , Rb , Cs O , Se , Te , Po , He, Xe , Kr , Br, At

We have to check which has negative electron gain enthalpy.

solution : electron gain enthalpy is the amount of heat released when we add one electron in an isolated gaseous atom.

For half filled and completely filled outermost orbit, electron gain enthalpy will be positive because it has require heat to add electron.

Here, He, Xe and Kr are noble gases so these have completely filled outermost orbits. So electron gain enthalpies for these are always positive.

Now rest elements have negative because

(H , Li , Na K, Rb , Cs ) belongs to 1st group ( ns¹) so we can easily add one electron.

(O, S, Se , Te , Po) belongs to oxygen family (np² ) so adding of electron, gives negative electron gain enthalpy.

And Br and At (Astatine) elements belomg to halogen family, have also negative electron gain enthalpies.

So there are 13 elements which have negative electron gain enthalpies