Question

the calculated electron gain enthalpy values for alkaline earth metals and noble gases are positive. how can you explain this?

Answer 1

alkaline earth metal which belong to group 2nd in periodic table and shows ns2 configuration which is fully filled and hence its is more stable than its corresponding group alkali metals. similarly in noble gases these are most stable elements or gases in periodic table having configuration ns2;np6.therefore energy required to remove an electron from there outermost shell is positive

Answer 2

The modren periodic table is based on the electronic configuration of element.

The eletronic configuration of llA group (alkaline earth metals) is ns2 the electrons are full filled in s-block it is not easy to remove electron from outer most orbit of the llA group elements hence the electron gain enthalpy values is positive

the electronic configuration of noble gases ns2and np6 in the electrones in s and p block are full filled . So, it is difficult to remove electron or add electron hence the electron gain enthalpy values of noble gases are positive.